Oracle Interview Questions - Part 7 Interview question

What should be the return type for a cursor variable.Can we use a scalar data type as return type?
The return type for a cursor must be a record type.It can be declared explicitly as a user-defined or %ROWTYPE can be used. eg TYPE t_studentsref IS REF CURSOR RETURN students%ROWTYPE

What are different Oracle database objects?
-TABLES
-VIEWS
-INDEXES
-SYNONYMS
-SEQUENCES
-TABLESPACES etc

What is difference between SUBSTR and INSTR?
SUBSTR returns a specified portion of a string eg SUBSTR('BCDEF',4) output BCDE INSTR provides character position in which a pattern is found in a string. eg INSTR('ABC-DC-F','-',2) output 7 (2nd occurence of '-')

Display the number value in Words?
SQL> select sal, (to_char(to_date(sal,'j'), 'jsp'))
from emp;
the output like,
SAL (TO_CHAR(TO_DATE(SAL,'J'),'JSP'))
--------- ----------------------------------------
800 eight hundred
1600 one thousand six hundred
1250 one thousand two hundred fifty
If you want to add some text like, Rs. Three Thousand only.
SQL> select sal "Salary ",
(' Rs. '|| (to_char(to_date(sal,'j'), 'Jsp'))|| ' only.'))
"Sal in Words" from emp
/
Salary Sal in Words
------- -----------------------------------------------
800 Rs. Eight Hundred only.
1600 Rs. One Thousand Six Hundred only.
1250 Rs. One Thousand Two Hundred Fifty only.

What is difference between SQL and SQL*PLUS?
SQL*PLUS is a command line tool where as SQL and PL/SQL language interface and reporting tool. Its a command line tool that allows user to type SQL commands to be executed directly against an Oracle database. SQL is a language used to query the relational database(DML,DCL,DDL). SQL*PLUS commands are used to format query result, Set options, Edit SQL commands and PL/SQL.

What are various joins used while writing SUBQUERIES?
Self join-Its a join foreign key of a table references the same table. Outer Join--Its a join condition used where One can query all the rows of one of the tables in the join condition even though they don't satisfy the join condition.
Equi-join--Its a join condition that retrieves rows from one or more tables in which one or more columns in one table are equal to one or more columns in the second table.

What a SELECT FOR UPDATE cursor represent.?
SELECT......FROM......FOR......UPDATE[OF column-reference][NOWAIT]
The processing done in a fetch loop modifies the rows that have been retrieved by the cursor. A convenient way of modifying the rows is done by a method with two parts: the FOR UPDATE clause in the cursor declaration, WHERE CURRENT OF CLAUSE in an UPDATE or declaration statement.

What are various privileges that a user can grant to another user?
-SELECT
-CONNECT
-RESOURCES

Display the records between two range?
select rownum, empno, ename from emp where rowid in (select rowid from emp where rownum <=&upto minus select rowid from emp where rownum<&Start); minvalue.sql Select the

Nth lowest value from a table?
select level, min('col_name') from my_table where level = '&n' connect by prior ('col_name') < 'col_name') group by level; Example: Given a table called emp with the following columns: -- id number -- name varchar2(20) -- sal number -- -- For the second lowest salary: -- select level, min(sal) from emp -- where level=2 -- connect by prior sal <>What is difference between Rename and Alias?
Rename is a permanent name given to a table or column whereas Alias is a temporary name given to a table or column which do not exist once the SQL statement is executed.

Difference between an implicit & an explicit cursor.?
only one row. However,queries that return more than one row you must declare an explicit cursor or use a cursor FOR loop. Explicit cursor is a cursor in which the cursor name is explicitly assigned to a SELECT statement via the CURSOR...IS statement. An implicit cursor is used for all SQL statements Declare, Open, Fetch, Close. An explicit cursors are used to process multirow SELECT statements An implicit cursor is used to process INSERT, UPDATE, DELETE and single row SELECT. .INTO statements.

What is a OUTER JOIN?
Outer Join--Its a join condition used where you can query all the rows of one of the tables in the join condition even though they don’t satisfy the join condition.

What is a cursor?
Oracle uses work area to execute SQL statements and store processing information PL/SQL construct called a cursor lets you name a work area and access its stored information A cursor is a mechanism used to fetch more than one row in a Pl/SQl block.

What is the purpose of a cluster?
Oracle does not allow a user to specifically locate tables, since that is a part of the function of the RDBMS. However, for the purpose of increasing performance, oracle allows a developer to create a CLUSTER. A CLUSTER provides a means for storing data from different tables together for faster retrieval than if the table placement were left to the RDBMS.

What is OCI. What are its uses?
Oracle Call Interface is a method of accesing database from a 3GL program. Uses--No precompiler is required,PL/SQL blocks are executed like other DML statements.
The OCI library provides
--functions to parse SQL statemets
--bind input variables
--bind output variables
--execute statements
--fetch the results

How you open and close a cursor variable.Why it is required?
OPEN cursor variable FOR SELECT...Statement
CLOSE cursor variable In order to associate a cursor variable with a particular SELECT statement OPEN syntax is used. In order to free the resources used for the query CLOSE statement is used.

Display Odd/ Even number of records?
Odd number of records:
select * from emp where (rowid,1) in (select rowid, mod(rownum,2) from emp);
Output:-
1
3
5
Even number of records:
select * from emp where (rowid,0) in (select rowid, mod(rownum,2) from emp)
Output:-
2
4
6

What are various constraints used in SQL?
-NULL
-NOT NULL
-CHECK
-DEFAULT

Can cursor variables be stored in PL/SQL tables.If yes how. If not why?
No, a cursor variable points a row which cannot be stored in a two-dimensional PL/SQL table.

Difference between NO DATA FOUND and %NOTFOUND?
NO DATA FOUND is an exception raised only for the SELECT....INTO statements when the where clause of the querydoes not match any rows. When the where clause of the explicit cursor does not match any rows the %NOTFOUND attribute is set to TRUE instead.

Can you use a commit statement within a database trigger?
No

What WHERE CURRENT OF clause does in a cursor?
LOOP
SELECT num_credits INTO v_numcredits FROM classes
WHERE dept=123 and course=101;
UPDATE students
FHKO;;;;;;;;;SET current_credits=current_credits+v_numcredits
WHERE CURRENT OF X;

There is a string 120000 12 0 .125 , how you will find the position of the decimal place?
INSTR('120000 12 0 .125',1,'.')
output 13

What are different modes of parameters used in functions and procedures?
-IN -OUT -INOUT

How you were passing cursor variables in PL/SQL 2.2?
In PL/SQL 2.2 cursor variables cannot be declared in a package.This is because the storage for a cursor variable has to be allocated using Pro*C or OCI with version 2.2, the only means of passing a cursor variable to a PL/SQL block is via bind variable or a procedure parameter.

When do you use WHERE clause and when do you use HAVING clause?
HAVING clause is used when you want to specify a condition for a group function and it is written after GROUP BY clause. The WHERE clause is used when you want to specify a condition for columns, single row functions except group functions and it is written before GROUP BY clause if it is used.

Difference between procedure and function.?
Functions are named PL/SQL blocks that return a value and can be called with arguments procedure a named block that can be called with parameter. A procedure all is a PL/SQL statement by itself, while a Function call is called as part of an expression.

Which is more faster - IN or EXISTS?
EXISTS is more faster than IN because EXISTS returns a Boolean value whereas IN returns a value.

What is syntax for dropping a procedure and a function .Are these operations possible?
Drop Procedure procedure_name
Drop Function function_name

How will you delete duplicating rows from a base table?
delete from table_name where rowid not in (select max(rowid) from table group by duplicate_values_field_name); or delete duplicate_values_field_name dv from table_name ta where rowid <(select min(rowid) from table_name tb where ta.dv=tb.dv); Difference between database triggers and form triggers?
-Data base trigger(DBT) fires when a DML operation is performed on a data base table. Form trigger(FT) Fires when user presses a key or navigates between fields on the screen
-Can be row level or statement level No distinction between row level and statement level.
-Can manipulate data stored in Oracle tables via SQL Can manipulate data in Oracle tables as well as variables in forms.
-Can be fired from any session executing the triggering DML statements. Can be fired only from the form that define the trigger.
-Can cause other database triggers to fire.Can cause other database triggers to fire, but not other form triggers.

What is a cursor for loop?
Cursor For Loop is a loop where oracle implicitly declares a loop variable, the loop index that of the same record type as the cursor's record.

How you will avoid duplicating records in a query?
By using DISTINCT

What is a view ?
A view is stored procedure based on one or more tables, it’s a virtual table.

What is difference between UNIQUE and PRIMARY KEY constraints?
A table can have only one PRIMARY KEY whereas there can be any number of UNIQUE keys. The columns that compose PK are automatically define NOT NULL, whereas a column that compose a UNIQUE is not automatically defined to be mandatory must also specify the column is NOT NULL.

What is use of a cursor variable? How it is defined?
A cursor variable is associated with different statements at run time, which can hold different values at run time. Static cursors can only be associated with one run time query. A cursor variable is reference type (like a pointer in C).
Declaring a cursor variable:
TYPE type_name IS REF CURSOR RETURN return_type type_name is the name of the reference type,return_type is a record type indicating the types of the select list that will eventually be returned by the cursor variable.

How do you find the numbert of rows in a Table ?
A bad answer is count them (SELECT COUNT(*) FROM table_name)
A good answer is :-
'By generating SQL to ANALYZE TABLE table_name COUNT STATISTICS by querying Oracle System Catalogues (e.g. USER_TABLES or ALL_TABLES).
The best answer is to refer to the utility which Oracle released which makes it unnecessary to do ANALYZE TABLE for each Table individually.

What is the maximum buffer size that can be specified using the DBMS_OUTPUT.ENABLE function?
1,000,00

What are cursor attributes?
-%ROWCOUNT
-%NOTFOUND
-%FOUND
-%ISOPEN

There is a % sign in one field of a column. What will be the query to find it?
'' Should be used before '%'.

What is ON DELETE CASCADE ?
When ON DELETE CASCADE is specified ORACLE maintains referential integrity by automatically removing dependent foreign key values if a referenced primary or unique key value is removed.

What is the fastest way of accessing a row in a table ?
Using ROWID.CONSTRAINTS

What is difference between TRUNCATE & DELETE ?
TRUNCATE commits after deleting entire table i.e., can not be rolled back. Database triggers do not fire on TRUNCATEDELETE allows the filtered deletion. Deleted records can be rolled back or committed.Database triggers fire on DELETE.

What is a transaction ?
Transaction is logical unit between two commits and commit and rollback.

What are the advantages of VIEW ?
To protect some of the columns of a table from other users.To hide complexity of a query.To hide complexity of calculations.

How will you a activate/deactivate integrity constraints ?
The integrity constraints can be enabled or disabled by ALTER TABLE ENABLE constraint/DISABLE constraint.

Where the integrity constraints are stored in Data Dictionary ?
The integrity constraints are stored in USER_CONSTRAINTS.

What is the Subquery ?
Sub query is a query whose return values are used in filtering conditions of the main query.

How to access the current value and next value from a sequence ? Is it possible to access the current value in a session before accessing next value ?
Sequence name CURRVAL, Sequence name NEXTVAL.It is not possible. Only if you access next value in the session, current value can be accessed.

What are the usage of SAVEPOINTS ?value in a session before accessing next value ?
SAVEPOINTS are used to subdivide a transaction into smaller parts. It enables rolling back part of a transaction. Maximum of five save points are allowed.

What is ROWID ?in a session before accessing next value ?
ROWID is a pseudo column attached to each row of a table. It is 18 character long, blockno, rownumber are the components of ROWID.

Explain Connect by Prior ?in a session before accessing next value ?
Retrieves rows in hierarchical order.e.g. select empno, ename from emp where.

How many LONG columns are allowed in a table ? Is it possible to use LONG columns in WHERE clause or ORDER BY ?
Only one LONG columns is allowed. It is not possible to use LONG column in WHERE or ORDER BY clause.

What is Referential Integrity ?
Maintaining data integrity through a set of rules that restrict the values of one or more columns of the tables based on the values of primary key or unique key of the referenced table.

What is a join ? Explain the different types of joins ?
Join is a query which retrieves related columns or rows from multiple tables.Self Join - Joining the table with itself.Equi Join - Joining two tables by equating two common columns.Non-Equi Join - Joining two tables by equating two common columns.Outer Join - Joining two tables in such a way that query can also retrieve rows that do not have corresponding join value in the other table.

If an unique key constraint on DATE column is created, will it validate the rows that are inserted with SYSDATE ?
It won't, Because SYSDATE format contains time attached with it.

How does one stop and start the OMS? (for DBA)
Use the following command sequence to stop and start the OMS (Oracle Management Server):
oemctl start oms
oemctl status oms sysman/oem_temp
oemctl stop oms sysman/oem_temp
Windows NT/2000 users can just stop and start the required services. The default OEM administrator is "sysman" with a password of "oem_temp".
NOTE: Use command oemctrl instead of oemctl for Oracle 8i and below.

What is an Integrity Constraint ?
Integrity constraint is a rule that restricts values to a column in a table.

How does one create a repository? (for DBA)
For OEM v2 and above, start the Oracle Enterprise Manager Configuration Assistant (emca on Unix) to create and configure the management server and repository. Remember to setup a backup for the repository database after creating it.

If a View on a single base table is manipulated will the changes be reflected on the base table ?
If changes are made to the tables which are base tables of a view will the changes be reference on the view.

The following describes means to create a OEM V1.x (very old!!!) repository on WindowsNT:

. Create a tablespace that would hold the repository data. A size between 200- 250 MB would be ideal. Let us call it Dummy_Space.
. Create an Oracle user who would own this repository. Assign DBA, SNMPAgent, Exp_Full_database, Imp_Full_database roles to this user. Lets call this user Dummy_user. Assign Dummy_Space as the default tablespace.
. Create an operating system user with the same name as the Oracle username. I.e. Dummy_User. Add 'Log on as a batch job' under advanced rights in User manager.
. Fire up Enterprise manager and log in as Dummy_User and enter the password. This would trigger the creation of the repository. From now on, Enterprise manager is ready to accept jobs.

What is a database link ?
Database Link is a named path through which a remote database can be accessed.

How does one list one's databases in the OEM Console? (for DBA)
Follow these steps to discover databases and other services from the OEM Console:
1. Ensure the GLOBAL_DBNAME parameter is set for all databases in your LISTENER.ORA file (optional). These names will be listed in the OEM Console. Please note that names entered are case sensitive. A portion of a listener.ora file:
(SID_DESC =
(GLOBAL_DBNAME = DB_name_for_OEM)
(SID_NAME = ...
2. Start the Oracle Intelligent Agent on the machine you want to discover. See section "How does one start the Oracle Intelligent Agent?".
3. Start the OEM Console, navigate to menu "Navigator/ Discover Nodes". The OEM Discovery Wizard will guide you through the process of discovering your databases and other services.

What is CYCLE/NO CYCLE in a Sequence ?
CYCLE specifies that the sequence continues to generate values after reaching either maximum or minimum value. After pan ascending sequence reaches its maximum value, it generates its minimum value. After a descending sequence reaches its minimum, it generates its maximum.NO CYCLE specifies that the sequence cannot generate more values after reaching its maximum or minimum value.

What is correlated sub-query ?
Correlated sub query is a sub query which has reference to the main query.

What are the data types allowed in a table ?
CHAR,VARCHAR2,NUMBER,DATE,RAW,LONG and LONG RAW.

What is difference between CHAR and VARCHAR2 ? What is the maximum SIZE allowed for each type ?
CHAR pads blank spaces to the maximum length. VARCHAR2 does not pad blank spaces. For CHAR it is 255 and 2000 for VARCHAR2.

Can a view be updated/inserted/deleted? If Yes under what conditions ?
A View can be updated/deleted/inserted if it has only one base table if the view is based on columns from one or more tables then insert, update and delete is not possible.

What are the different types of Coordinations of the Master with the Detail block?
POPULATE_GROUP(function)
POPULATE_GROUP_WITH_QUERY(function)
SET_GROUP_CHAR_CELL(procedure)
SET_GROUPCELL(procedure)
SET_GROUP_NUMBER_CELL(procedure)

Use the ADD_GROUP_COLUMN function to add a column to a record group that was created at design time?
I) TRUE II) FALSE
II) FALSE

Use the ADD_GROUP_ROW procedure to add a row to a static record group?
I) TRUE II) FALSE
I) FALSE

maxvalue.sql Select the Nth Highest value from a table?
select level, max('col_name') from my_table where level = '&n' connect by prior ('col_name') > 'col_name')
group by level;
Example:
Given a table called emp with the following columns:
-- id number
-- name varchar2(20)
-- sal number
--
-- For the second highest salary:
-- select level, max(sal) from emp
-- where level=2
-- connect by prior sal > sal
-- group by level

Find out nth highest salary from emp table?
SELECT DISTINCT (a.sal) FROM EMP A WHERE &N = (SELECT COUNT (DISTINCT (b.sal)) FROM EMP B WHERE a.sal<=b.sal); For E.g.:- Enter value for n: 2 SAL --------- 3700 Suppose a customer table is having different columns like customer no, payments.What will be the query to select top three max payments?
SELECT customer_no, payments from customer C1
WHERE 3<=(SELECT COUNT(*) from customer C2 WHERE C1.payment <= C2.payment) How you will avoid your query from using indexes?
SELECT * FROM emp
Where emp_no+' '=12345;
i.e you have to concatenate the column name with space within codes in the where condition.
SELECT /*+ FULL(a) */ ename, emp_no from emp
where emp_no=1234;
i.e using HINTS

What utility is used to create a physical backup?
Either rman or alter tablespace begin backup will do..

What are the Back ground processes in Oracle and what are they.
This is one of the most frequently asked question.There are basically 9 Processes but in a general system we need to mention the first five background processes.They do the house keeping activities for the Oracle and are common in any system.
The various background processes in oracle are
a) Data Base Writer(DBWR) :: Data Base Writer Writes Modified blocks from Database buffer cache to Data Files.This is required since the data is not written whenever a transaction is committed.
b)LogWriter(LGWR) :: LogWriter writes the redo log entries to disk. Redo Log data is generated in redo log buffer of SGA. As transaction commits and log buffer fills, LGWR writes log entries into a online redo log file.
c) System Monitor(SMON) :: The System Monitor performs instance recovery at instance startup. This is useful for recovery from system failure
d)Process Monitor(PMON) :: The Process Monitor performs process recovery when user Process fails. Pmon Clears and Frees resources that process was using.
e) CheckPoint(CKPT) :: At Specified times, all modified database buffers in SGA are written to data files by DBWR at Checkpoints and Updating all data files and control files of database to indicate the most recent checkpoint
f)Archieves(ARCH) :: The Archiver copies online redo log files to archival storal when they are busy.
g) Recoveror(RECO) :: The Recoveror is used to resolve the distributed transaction in network
h) Dispatcher (Dnnn) :: The Dispatcher is useful in Multi Threaded Architecture
i) Lckn :: We can have upto 10 lock processes for inter instance locking in parallel sql.

How many types of Sql Statements are there in Oracle
There are basically 6 types of sql statments.They are
a) Data Definition Language(DDL) :: The DDL statements define and maintain objects and drop objects.
b) Data Manipulation Language(DML) :: The DML statements manipulate database data.
c) Transaction Control Statements :: Manage change by DML
d) Session Control :: Used to control the properties of current session enabling and disabling roles and changing .e.g. :: Alter Statements, Set Role
e) System Control Statements :: Change Properties of Oracle Instance .e.g.:: Alter System
f) Embedded Sql :: Incorporate DDL, DML and T.C.S in Programming Language.e.g:: Using the Sql Statements in languages such as 'C', Open, Fetch, execute and close

What is a Transaction in Oracle
A transaction is a Logical unit of work that compromises one or more SQL Statements executed by a single User. According to ANSI, a transaction begins with first executable statement and ends when it is explicitly committed or rolled back.

Key Words Used in Oracle
The Key words that are used in Oracle are ::
a) Committing :: A transaction is said to be committed when the transaction makes permanent changes resulting from the SQL statements.
b) Rollback :: A transaction that retracts any of the changes resulting from SQL statements in Transaction.
c) SavePoint :: For long transactions that contain many SQL statements, intermediate markers or savepoints are declared. Savepoints can be used to divide a transaction into smaller points.
d) Rolling Forward :: Process of applying redo log during recovery is called rolling forward.
e) Cursor :: A cursor is a handle ( name or a pointer) for the memory associated with a specific stamen. A cursor is basically an area allocated by Oracle for executing the Sql Statement. Oracle uses an implicit cursor statement for Single row query and Uses Explicit cursor for a multi row query.
f) System Global Area(SGA) :: The SGA is a shared memory region allocated by the Oracle that contains Data and control information for one Oracle Instance. It consists of Database Buffer Cache and Redo log Buffer.
g) Program Global Area (PGA) :: The PGA is a memory buffer that contains data and control information for server process.
g) Database Buffer Cache :: Database Buffer of SGA stores the most recently used blocks of database data. The set of database buffers in an instance is called Database Buffer Cache.
h) Redo log Buffer :: Redo log Buffer of SGA stores all the redo log entries.
i) Redo Log Files :: Redo log files are set of files that protect altered database data in memory that has not been written to Data Files. They are basically used for backup when a database crashes.
j) Process :: A Process is a 'thread of control' or mechanism in Operating System that executes series of steps.

Oracle Interview Questions - Part 8 Interview question

What are the components of physical database structure of Oracle database?
Oracle database is comprised of three types of files. One or more datafiles, two are more redo log files, and one or more control files.

What are the components of logical database structure of Oracle database?
There are tablespaces and database's schema objects.

What is a tablespace?
A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together.

What is SYSTEM tablespace and when is it created?
Every Oracle database contains a tablespace named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database.

Explain the relationship among database, tablespace and data file ?
Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace.

What is schema?
A schema is collection of database objects of a user.

What are Schema Objects?
Schema objects are the logical structures that directly refer to the database's data. Schema objects include tables, views, sequences, synonyms, indexes, clusters, database triggers, procedures, functions packages and database links.

Can objects of the same schema reside in different tablespaces?
Yes.

Can a tablespace hold objects from different schemes?
Yes.

What is Oracle table?
A table is the basic unit of data storage in an Oracle database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.

What is an Oracle view?
A view is a virtual table. Every view has a query attached to it. (The query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)

What is Partial Backup ?
A Partial Backup is any operating system backup short of a full backup, taken while the database is open or shut down.

What is Mirrored on-line Redo Log ?
A mirrored on-line redo log consists of copies of on-line redo log files physically located on separate disks, changes made to one member of the group are made to all members

What is Full Backup ?
A full backup is an operating system backup of all data files, on-line redo log files and control file that constitute ORACLE database and the parameter.

Can a View based on another View ?
Yes.

Can a Tablespace hold objects from different Schemes ?
Yes.

Can objects of the same Schema reside in different tablespace ?
Yes.

What is the use of Control File ?
When an instance of an ORACLE database is started, its control file is used to identify the database and redo log files that must be opened for database operation to proceed. It is also used in database recovery.

Do View contain Data ?
Views do not contain or store data.

What are the Referential actions supported by FOREIGN KEY integrity constraint ?
UPDATE and DELETE Restrict - A referential integrity rule that disallows the update or deletion of referenced data. DELETE Cascade - When a referenced row is deleted all associated dependent rows are deleted.

What are the type of Synonyms?
There are two types of Synonyms Private and Public.

What is a Redo Log ?
The set of Redo Log files YSDATE,UID,USER or USERENV SQL functions, or the pseudo columns LEVEL or ROWNUM.

What is an Index Segment ?
Each Index has an Index segment that stores all of its data.

Explain the relationship among Database, Tablespace and Data file?
Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace

What are the different type of Segments ?
Data Segment, Index Segment, Rollback Segment and Temporary Segment.

What are Clusters ?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.

What is an Integrity Constrains ?
An integrity constraint is a declarative way to define a business rule for a column of a table.

What is an Index ?
An Index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.

What is an Extent ?
An Extent is a specific number of contiguous data blocks, obtained in a single allocation, and used to store a specific type of information.

What is a View ?
A view is a virtual table. Every view has a Query attached to it. (The Query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)

What is Table ?
A table is the basic unit of data storage in an ORACLE database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.

What are snap shots and views
Snapshots are mirror or replicas of tables. Views are built using the columns from one or more tables. The Single Table View can be updated but the view with multi table cannot be updated

What are the OOPS concepts in Oracle.
Oracle does implement the OOPS concepts. The best example is the Property Classes. We can categorise the properties by setting the visual attributes and then attach the property classes for the objects. OOPS supports the concepts of objects and classes and we can consider the peroperty classes as classes and the items as objects

What is the difference between candidate key, unique key and primary key
Candidate keys are the columns in the table that could be the primary keys and the primary key is the key that has been selected to identify the rows. Unique key is also useful for identifying the distinct rows in the table.)

What is concurrency
Concurrency is allowing simultaneous access of same data by different users. Locks useful for accesing the database are
a) Exclusive
The exclusive lock is useful for locking the row when an insert,update or delete is being done.This lock should not be applied when we do only select from the row.
b) Share lock
We can do the table as Share_Lock as many share_locks can be put on the same resource.

Previleges and Grants
Previleges are the right to execute a particulare type of SQL statements. e.g :: Right to Connect, Right to create, Right to resource Grants are given to the objects so that the object might be accessed accordingly.The grant has to be given by the owner of the object

Table Space,Data Files,Parameter File, Control Files

Table Space :: The table space is useful for storing the data in the database.When a database is created two table spaces are created.
a) System Table space :: This data file stores all the tables related to the system and dba tables
b) User Table space :: This data file stores all the user related tables
We should have seperate table spaces for storing the tables and indexes so that the access is fast.
Data Files :: Every Oracle Data Base has one or more physical data files.They store the data for the database.Every datafile is associated with only one database.Once the Data file is created the size cannot change.To increase the size of the database to store more data we have to add data file.
Parameter Files :: Parameter file is needed to start an instance.A parameter file contains the list of instance configuration parameters e.g.::
db_block_buffers = 500
db_name = ORA7
db_domain = u.s.acme lang
Control Files :: Control files record the physical structure of the data files and redo log files
They contain the Db name, name and location of dbs, data files ,redo log files and time stamp.

Physical Storage of the Data
The finest level of granularity of the data base are the data blocks.
Data Block :: One Data Block correspond to specific number of physical database space
Extent :: Extent is the number of specific number of contigious data blocks.
Segments :: Set of Extents allocated for Extents. There are three types of Segments
a) Data Segment :: Non Clustered Table has data segment data of every table is stored in cluster data segment
b) Index Segment :: Each Index has index segment that stores data
c) Roll Back Segment :: Temporarily store 'undo' information

What are the Pct Free and Pct Used
Pct Free is used to denote the percentage of the free space that is to be left when creating a table. Similarly Pct Used is used to denote the percentage of the used space that is to be used when creating a table
eg.:: Pctfree 20, Pctused 40

What is Row Chaining
The data of a row in a table may not be able to fit the same data block.Data for row is stored in a chain of data blocks .

What is a 2 Phase Commit
Two Phase commit is used in distributed data base systems. This is useful to maintain the integrity of the database so that all the users see the same values. It contains DML statements or Remote Procedural calls that reference a remote object. There are basically 2 phases in a 2 phase commit.
a) Prepare Phase :: Global coordinator asks participants to prepare
b) Commit Phase :: Commit all participants to coordinator to Prepared, Read only or abort Reply

What is the difference between deleting and truncating of tables
Deleting a table will not remove the rows from the table but entry is there in the database dictionary and it can be retrieved But truncating a table deletes it completely and it cannot be retrieved.

What are mutating tables
When a table is in state of transition it is said to be mutating. eg :: If a row has been deleted then the table is said to be mutating and no operations can be done on the table except select.

What are Codd Rules
Codd Rules describe the ideal nature of a RDBMS. No RDBMS satisfies all the 12 codd rules and Oracle Satisfies 11 of the 12 rules and is the only Rdbms to satisfy the maximum number of rules.

What is Normalisation
Normalisation is the process of organising the tables to remove the redundancy.There are mainly 5 Normalisation rules.
a) 1 Normal Form :: A table is said to be in 1st Normal Form when the attributes are atomic
b) 2 Normal Form :: A table is said to be in 2nd Normal Form when all the candidate keys are dependant on the primary key
c) 3rd Normal Form :: A table is said to be third Normal form when it is not dependant transitively

What is the Difference between a post query and a pre query
A post query will fire for every row that is fetched but the pre query will fire only once.

Deleting the Duplicate rows in the table
We can delete the duplicate rows in the table by using the Rowid

Can U disable database trigger? How?
Yes. With respect to table
ALTER TABLE TABLE
[[ DISABLE all_trigger ]]

What is pseudo columns ? Name them?
A pseudocolumn behaves like a table column, but is not actually stored in the table. You can select from pseudocolumns, but you cannot insert, update, or delete their values. This section describes these pseudocolumns:
* CURRVAL
* NEXTVAL
* LEVEL
* ROWID
* ROWNUM

How many columns can table have?
The number of columns in a table can range from 1 to 254.

Is space acquired in blocks or extents ?
In extents .

What is clustered index?
In an indexed cluster, rows are stored together based on their cluster key values . Can not applied for HASH.

What are the datatypes supported By oracle (INTERNAL)?
Varchar2, Number,Char , MLSLABEL.

What are attributes of cursor?
%FOUND , %NOTFOUND , %ISOPEN,%ROWCOUNT

Can you use select in FROM clause of SQL select ?
Yes.

Which trigger are created when master -detail relay?
master delete property
* NON-ISOLATED (default)
a) on check delete master
b) on clear details
c) on populate details
* ISOLATED
a) on clear details
b) on populate details
* CASCADE
a) per-delete
b) on clear details
c) on populate details

which system variables can be set by users?
SYSTEM.MESSAGE_LEVEL
SYSTEM.DATE_THRESHOLD
SYSTEM.EFFECTIVE_DATE
SYSTEM.SUPPRESS_WORKING

What are object group?
An object group is a container for a group of objects. You define an object group when you want to package related objects so you can copy or reference them in another module.

What are referenced objects?
Referencing allows you to create objects that inherit their functionality and appearance from other objects. Referencing an object is similar to copying an object, except that the resulting reference object maintains a link to its source object. A reference object automatically inherits any changes that have been made to the source object when you open or regenerate the module that contains the reference object.

Can you store objects in library?
Referencing allows you to create objects that inherit their functionality and appearance from other objects. Referencing an object is similar to copying an object, except that the resulting reference object maintains a link to its source object. A reference object automatically inherits any changes that have been made to the source object when you open or regenerate the module that contains the reference object.

Is forms 4.5 object oriented tool ? why?
yes , partially. 1) PROPERTY CLASS - inheritance property 2) OVERLOADING : procedures and functions.

Can you issue DDL in forms?
yes, but you have to use FORMS_DDL.
Referencing allows you to create objects that inherit their functionality and appearance from other objects. Referencing an object is similar to copying an object, except that the resulting reference object maintains a link to its source object. A reference object automatically inherits any changes that have been made to the source object when you open or regenerate the module that contains the reference object. Any string expression up to 32K:
- a literal
- an expression or a variable representing the text of a block of dynamically created PL/SQL code
- a DML statement or
- a DDL statement
Restrictions:
The statement you pass to FORMS_DDL may not contain bind variable references in the string, but the values of bind variables can be concatenated into the string before passing the result to FORMS_DDL.

What is SECURE property?
- Hides characters that the operator types into the text item. This setting is typically used for password protection.

What are the types of triggers and how the sequence of firing in text item
Triggers can be classified as Key Triggers, Mouse Triggers ,Navigational Triggers.
Key Triggers :: Key Triggers are fired as a result of Key action.e.g :: Key-next-field, Key-up,Key-Down
Mouse Triggers :: Mouse Triggers are fired as a result of the mouse navigation.e.g. When-mouse-button-presed,when-mouse-doubleclicked,etc
Navigational Triggers :: These Triggers are fired as a result of Navigation. E.g. : Post-Text-item,Pre-text-item.
We also have event triggers like when ?new-form-instance and when-new-block-instance.
We cannot call restricted procedures like go_to(?my_block.first_item?) in the Navigational triggers
But can use them in the Key-next-item.
The Difference between Key-next and Post-Text is an very important question. The key-next is fired as a result of the key action while the post text is fired as a result of the mouse movement. Key next will not fire unless there is a key event. The sequence of firing in a text item are as follows ::
a) pre - text
b) when new item
c) key-next
d) when validate
e) post text

Can you store pictures in database? How?
Yes , in long Raw datatype.

What are property classes ? Can property classes have trigger?
Property class inheritance is a powerful feature that allows you to quickly define objects that conform to your own interface and functionality standards. Property classes also allow you to make global changes to applications quickly. By simply changing the definition of a property class, you can change the definition of all objects that inherit properties from that class.
Yes . All type of triggers .

If you have property class attached to an item and you have same trigger written for the item . Which will fire first?
Item level trigger fires , If item level trigger fires, property level trigger won't fire. Triggers at the lowest level are always given the first preference. The item level trigger fires first and then the block and then the Form level trigger.

What are record groups ? * Can record groups created at run-time?
A record group is an internal Oracle Forms data structure that has a column/row framework similar to a database table. However, unlike database tables, record groups are separate objects that belong to the form module in which they are defined. A record group can have an unlimited number of columns of type CHAR, LONG, NUMBER, or DATE provided that the total number of columns does not exceed 64K. Record group column names cannot exceed 30 characters.
Programmatically, record groups can be used whenever the functionality offered by a two-dimensional array of multiple data types is desirable.
TYPES OF RECORD GROUP:
Query Record Group A query record group is a record group that has an associated SELECT statement. The columns in a query record group derive their default names, data types, and lengths from the database columns referenced in the SELECT statement. The records in a query record group are the rows retrieved by the query associated with that record group.
Non-query Record Group A non-query record group is a group that does not have an associated query, but whose structure and values can be modified programmatically at runtime.
Static Record Group A static record group is not associated with a query; rather, you define its structure and row values at design time, and they remain fixed at runtime.

What are ALERT?
An ALERT is a modal window that displays a message notifying operator of some application condition.

Can a button have icon and label at the same time ?
-NO

What is mouse navigate property of button?
When Mouse Navigate is True (the default), Oracle Forms performs standard navigation to move the focus to the item when the operator activates the item with the mouse.
When Mouse Navigate is set to False, Oracle Forms does not perform navigation (and the resulting validation) to move to the item when an operator activates the item with the mouse.

What is FORMS_MDI_WINDOW?
forms run inside the MDI application window. This property is useful for calling a form from another one.

What are timers ? when when-timer-expired does not fire?
The When-Timer-Expired trigger can not fire during trigger, navigation, or transaction processing.

Can object group have a block?
Yes , object group can have block as well as program units.

How many types of canvases are there.
There are 2 types of canvases called as Content and Stack Canvas. Content canvas is the default and the one that is used mostly for giving the base effect. Its like a plate on which we add items and stacked canvas is used for giving 3 dimensional effect.

What are user-exits?
It invokes 3GL programs.

Can you pass values to-and-fro from foreign function ? how ?
Yes . You obtain a return value from a foreign function by assigning the return value to an Oracle Forms variable or item. Make sure that the Oracle Forms variable or item is the same data type as the return value from the foreign function.
After assigning an Oracle Forms variable or item value to a PL/SQL variable, pass the PL/SQL variable as a parameter value in the PL/SQL interface of the foreign function. The PL/SQL variable that is passed as a parameter must be a valid PL/SQL data type; it must also be the appropriate parameter type as defined in the PL/SQL interface.

What is IAPXTB structure ?
The entries of Pro * C and user exits and the form which simulate the proc or user_exit are stored in IAPXTB table in d/b.

Can you call WIN-SDK thru user exits?
YES.

Oracle Interview Questions - Part 9 Interview question

Does user exits supports DLL on MSWINDOWS ?
YES .

What is path setting for DLL?
Make sure you include the name of the DLL in the FORMS45_USEREXIT variable of the ORACLE.INI file, or rename the DLL to F45XTB.DLL. If you rename the DLL to F45XTB.DLL, replace the existing F45XTB.DLL in the ORAWINBIN directory with the new F45XTB.DLL.

How is mapping of name of DLL and function done?
The dll can be created using the Visual C++ / Visual Basic Tools and then the dll is put in the path that is defined the registery.

What is precompiler?
It is similar to C precompiler directives.

Can you connect to non - oracle datasource ? How?
Yes .

What are key-mode and locking mode properties? level ?
Key Mode : Specifies how oracle forms uniquely identifies rows in the database.This is property includes for application that will run against NON-ORACLE datasources .
Key setting unique (default.)
dateable
n-updateable.
Locking mode :
Specifies when Oracle Forms should attempt to obtain database locks on rows that correspond to queried records in the form. a) immediate b) delayed

What are savepoint mode and cursor mode properties ? level?
Specifies whether Oracle Forms should issue savepoints during a session. This property is included primarily for applications that will run against non-ORACLE data sources. For applications that will run against ORACLE, use the default setting.
Cursor mode - define cursur state across transaction Open/close.

What is transactional trigger property?
Identifies a block as transactional control block. i.e. non - database block that oracle forms should manage as transactional block.(NON-ORACLE datasource) default - FALSE.

What is OLE automation ?
OLE automation allows an OLE server application to expose a set of commands and functions that can be invoked from an OLE container application. OLE automation provides a way for an OLE container application to use the features of an OLE server application to manipulate an OLE object from the OLE container environment. (FORMS_OLE)

What does invoke built-in do?
This procedure invokes a method.
Syntax:
PROCEDURE OLE2.INVOKE
(object obj_type,
method VARCHAR2,
list list_type := 0);
Parameters:
object Is an OLE2 Automation Object.
method Is a method (procedure) of the OLE2 object.
list Is the name of an argument list assigned to the OLE2.CREATE_ARGLIST function.

What are OPEN_FORM,CALL_FORM,NEW_FORM? diff?
CALL_FORM : It calls the other form. but parent remains active, when called form completes the operation , it releases lock and control goes back to the calling form.
When you call a form, Oracle Forms issues a savepoint for the called form. If the CLEAR_FORM function causes a rollback when the called form is current, Oracle Forms rolls back uncommitted changes to this savepoint.
OPEN_FORM : When you call a form, Oracle Forms issues a savepoint for the called form. If the CLEAR_FORM function causes a rollback when the called form is current, Oracle Forms rolls back uncommitted changes to this savepoint.
NEW_FORM : Exits the current form and enters the indicated form. The calling form is terminated as the parent form. If the calling form had been called by a higher form, Oracle Forms keeps the higher call active and treats it as a call to the new form. Oracle Forms releases memory (such as database cursors) that the terminated form was using.
Oracle Forms runs the new form with the same Runform options as the parent form. If the parent form was a called form, Oracle Forms runs the new form with the same options as the parent form.

What is call form stack?
When successive forms are loaded via the CALL_FORM procedure, the resulting module hierarchy is known as the call form stack.

Can u port applictions across the platforms? how?
Yes we can port applications across platforms.Consider the form developed in a windows system.The form would be generated in unix system by using f45gen my_form.fmb scott/tiger

What is a visual attribute?
Visual attributes are the font, color, and pattern properties that you set for form and menu objects that appear in your application's interface.

Diff. between VAT and Property Class?
Named visual attributes define only font, color, and pattern attributes; property classes can contain these and any other properties.
You can change the appearance of objects at runtime by changing the named visual attribute programmatically; property class assignment cannot be changed programmatically. When an object is inheriting from both a property class and a named visual attribute, the named visual attribute settings take precedence, and any visual attribute properties in the class are ignored.

Which trigger related to mouse?
When-Mouse-Click
When-Mouse-DoubleClick
When-Mouse-Down
When-Mouse-Enter
When-Mouse-Leave
When-Mouse-Move
When-Mouse-Up

What is Current record attribute property?
Specifies the named visual attribute used when an item is part of the current record. Current Record Attribute is frequently used at the block level to display the current row in a multi-record If you define an item-level Current Record Attribute, you can display a pre-determined item in a special color when it is part of the current record, but you cannot dynamically highlight the current item, as the input focus changes.

Can u change VAT at run time?
Yes. You can programmatically change an object's named visual attribute setting to change the font, color, and pattern of the object at runtime.

Can u set default font in forms?
Yes. Change windows registry(regedit). Set form45_font to the desired font.
_break

What is Log Switch ?
The point at which ORACLE ends writing to one online redo log file and begins writing to another is called a log switch.

What is On-line Redo Log?
The On-line Redo Log is a set of tow or more on-line redo files that record all committed changes made to the database. Whenever a transaction is committed, the corresponding redo entries temporarily stores in redo log buffers of the SGA are written to an on-line redo log file by the background process LGWR. The on-line redo log files are used in cyclical fashion.

Which parameter specified in the DEFAULT STORAGE clause of CREATE TABLESPACE cannot be altered after creating the tablespace?
All the default storage parameters defined for the tablespace can be changed using the ALTER TABLESPACE command. When objects are created their INITIAL and MINEXTENS values cannot be changed.

What are the steps involved in Database Startup ?
Start an instance, Mount the Database and Open the Database.
Rolling forward to recover data that has not been recorded in data files, yet has been recorded in the on-line redo log, including the contents of rollback segments. Rolling back transactions that have been explicitly rolled back or have not been committed as indicated by the rollback segments regenerated in step a. Releasing any resources (locks) held by transactions in process at the time of the failure. Resolving any pending distributed transactions undergoing a two-phase commit at the time of the instance failure.

Can Full Backup be performed when the database is open ?
No.

What are the different modes of mounting a Database with the Parallel Server ?
Exclusive Mode If the first instance that mounts a database does so in exclusive mode, only that Instance can mount the database.
Parallel Mode If the first instance that mounts a database is started in parallel mode, other instances that are started in parallel mode can also mount the database.

What are the advantages of operating a database in ARCHIVELOG mode over operating it in NO ARCHIVELOG mode ?
Complete database recovery from disk failure is possible only in ARCHIVELOG mode. Online database backup is possible only in ARCHIVELOG mode.

What are the steps involved in Database Shutdown ?
Close the Database, Dismount the Database and Shutdown the Instance.

What is Archived Redo Log ?
Archived Redo Log consists of Redo Log files that have archived before being reused.

What is Restricted Mode of Instance Startup ?
An instance can be started in (or later altered to be in) restricted mode so that when the database is open connections are limited only to those whose user accounts have been granted the RESTRICTED SESSION system privilege.

Can u have OLE objects in forms?
Yes.

Can u have VBX and OCX controls in forms ?
Yes.

What r the types of windows (Window style)?
Specifies whether the window is a Document window or a Dialog window.

What is OLE Activation style property?
Specifies the event that will activate the OLE containing item.

Can u change the mouse pointer ? How?
Yes. Specifies the mouse cursor style. Use this property to dynamically change the shape of the cursor.

How many types of columns are there and what are they
Formula columns :: For doing mathematical calculations and returning one value Summary Columns :: For doing summary calculations such as summations etc. Place holder Columns :: These columns are useful for storing the value in a variable

Can u have more than one layout in report
It is possible to have more than one layout in a report by using the additional layout option in the layout editor.

Can u run the report with out a parameter form
Yes it is possible to run the report without parameter form by setting the PARAM value to Null

What is the lock option in reports layout
By using the lock option we cannot move the fields in the layout editor outside the frame. This is useful for maintaining the fields .

What is Flex
Flex is the property of moving the related fields together by setting the flex property on

What are the minimum number of groups required for a matrix report
The minimum of groups required for a matrix report are 4 e -----

What is a Synonym ?
A synonym is an alias for a table, view, sequence or program unit.

What is a Sequence ?
A sequence generates a serial list of unique numbers for numerical columns of a database's tables.

What is a Segment ?
A segment is a set of extents allocated for a certain logical structure.

What is schema?
A schema is collection of database objects of a User.

Describe Referential Integrity ?
A rule defined on a column (or set of columns) in one table that allows the insert or update of a row only if the value for the column or set of columns (the dependent value) matches a value in a column of a related table (the referenced value). It also specifies the type of data manipulation allowed on referenced data and the action to be performed on dependent data as a result of any action on referenced data.

What is Hash Cluster ?
A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stores together on disk.

What is a Private Synonyms ?
A Private Synonyms can be accessed only by the owner.

What is Database Link ?
A database link is a named object that describes a "path" from one database to another.

What is index cluster?
A cluster with an index on the cluster key.

What is hash cluster?
A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stores together on disk.

When can hash cluster used?
Hash clusters are better choice when a table is often queried with equality queries. For such queries the specified cluster key value is hashed. The resulting hash key value points directly to the area on disk that stores the specified rows.

When can hash cluster used?
Hash clusters are better choice when a table is often queried with equality queries. For such queries the specified cluster key value is hashed. The resulting hash key value points directly to the area on disk that stores the specified rows.

What are the types of database links?
Private database link, public database link & network database link.

What is private database link?
Private database link is created on behalf of a specific user. A private database link can be used only when the owner of the link specifies a global object name in a SQL statement or in the definition of the owner's views or procedures.

What is public database link?
Public database link is created for the special user group PUBLIC. A public database link can be used when any user in the associated database specifies a global object name in a SQL statement or object definition.

What is network database link?
Network database link is created and managed by a network domain service. A network database link can be used when any user of any database in the network specifies a global object name in a SQL statement or object definition.

What is data block?
Oracle database's data is stored in data blocks. One data block corresponds to a specific number of bytes of physical database space on disk.

How to define data block size?
A data block size is specified for each Oracle database when the database is created. A database users and allocated free database space in Oracle data blocks. Block size is specified in init.ora file and cannot be changed latter.

What is row chaining?
In circumstances, all of the data for a row in a table may not be able to fit in the same data block. When this occurs, the data for the row is stored in a chain of data block (one or more) reserved for that segment.

What is an extent?
An extent is a specific number of contiguous data blocks, obtained in a single allocation and used to store a specific type of information.

What are the different types of segments?
Data segment, index segment, rollback segment and temporary segment.

What is a data segment?
Each non-clustered table has a data segment. All of the table's data is stored in the extents of its data segment. Each cluster has a data segment. The data of every table in the cluster is stored in the cluster's data segment.

What is an index segment?
Each index has an index segment that stores all of its data.

What is rollback segment?
A database contains one or more rollback segments to temporarily store "undo" information.

What are the uses of rollback segment?
To generate read-consistent database information during database recovery and to rollback uncommitted transactions by the users.

What is a temporary segment?
Temporary segments are created by Oracle when a SQL statement needs a temporary work area to complete execution. When the statement finishes execution, the temporary segment extents are released to the system for future use.

What is a datafile?
Every Oracle database has one or more physical data files. A database's data files contain all the database data. The data of logical database structures such as tables and indexes is physically stored in the data files allocated for a database.

What are the characteristics of data files?
A data file can be associated with only one database. Once created a data file can't change size. One or more data files form a logical unit of database storage called a tablespace.

What is a redo log?
The set of redo log files for a database is collectively known as the database redo log.

What is the function of redo log?
The primary function of the redo log is to record all changes made to data.

What is the use of redo log information?
The information in a redo log file is used only to recover the database from a system or media failure prevents database data from being written to a database's data files.

What does a control file contains?
- Database name
- Names and locations of a database's files and redolog files.
- Time stamp of database creation.

What is the use of control file?
When an instance of an Oracle database is started, its control file is used to identify the database and redo log files that must be opened for database operation to proceed. It is also used in database recovery.

Is it possible to split the print reviewer into more than one region?
Yes

Is it possible to center an object horizontally in a repeating frame that has a variable horizontal size?
Yes

For a field in a repeating frame, can the source come from the column which does not exist in the data group which forms the base for the frame?
Yes

Can a field be used in a report without it appearing in any data group?
Yes

The join defined by the default data link is an outer join yes or no?
Yes

Can a formula column referred to columns in higher group?
Yes

Can a formula column be obtained through a select statement?
Yes

Is it possible to insert comments into sql statements return in the data model editor?
Yes

Is it possible to disable the parameter from while running the report?
Yes

When a form is invoked with call_form, Does oracle forms issues a save point?
Yes

Explain the difference between a hot backup and a cold backup and the benefits associated with each.
A hot backup is basically taking a backup of the database while it is still up and running and it must be in archive log mode. A cold backup is taking a backup of the database while it is shut down and does not require being in archive log mode. The benefit of taking a hot backup is that the database is still available for use while the backup is occurring and you can recover the database to any point in time. The benefit of taking a cold backup is that it is typically easier to administer the backup and recovery process. In addition, since you are taking cold backups the database does not require being in archive log mode and thus there will be a slight performance gain as the database is not cutting archive logs to disk.

You have just had to restore from backup and do not have any control files. How would you go about bringing up this database?
I would create a text based backup control file, stipulating where on disk all the data files where and then issue the recover command with the using backup control file clause.

How do you switch from an init.ora file to a spfile?
Issue the create spfile from pfile command.

Explain the difference between a data block, an extent and a segment.
A data block is the smallest unit of logical storage for a database object. As objects grow they take chunks of additional storage that are composed of contiguous data blocks. These groupings of contiguous data blocks are called extents. All the extents that an object takes when grouped together are considered the segment of the database object.

Give two examples of how you might determine the structure of the table DEPT.
Use the describe command or use the dbms_metadata.get_ddl package.

Where would you look for errors from the database engine?
In the alert log.

Compare and contrast TRUNCATE and DELETE for a table.
Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete.

Give the reasoning behind using an index.
Faster access to data blocks in a table.

Give the two types of tables involved in producing a star schema and the type of data they hold.
Fact tables and dimension tables. A fact table contains measurements while dimension tables will contain data that will help describe the fact tables.

What type of index should you use on a fact table?
A Bitmap index.

Give two examples of referential integrity constraints.
A primary key and a foreign key.

A table is classified as a parent table and you want to drop and re-create it. How would you do this without affecting the children tables?
Disable the foreign key constraint to the parent, drop the table, re-create the table, enable the foreign key constraint.

Explain the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits and disadvantages to each.
ARCHIVELOG mode is a mode that you can put the database in for creating a backup of all transactions that have occurred in the database so that you can recover to any point in time. NOARCHIVELOG mode is basically the absence of ARCHIVELOG mode and has the disadvantage of not being able to recover to any point in time. NOARCHIVELOG mode does have the advantage of not having to write transactions to an archive log and thus increases the performance of the database slightly.

Oracle Interview Questions - Part 10 Interview question

What command would you use to create a backup control file?
Alter database backup control file to trace.

Give the stages of instance startup to a usable state where normal users may access it.
STARTUP NOMOUNT - Instance startup
STARTUP MOUNT - The database is mounted
STARTUP OPEN - The database is opened

What column differentiates the V$ views to the GV$ views and how?
The INST_ID column which indicates the instance in a RAC environment the information came from.

How would you go about generating an EXPLAIN plan?
Create a plan table with utlxplan.sql.
Use the explain plan set statement_id = 'tst1' into plan_table for a SQL statement
Look at the explain plan with utlxplp.sql or utlxpls.sql

How would you go about increasing the buffer cache hit ratio?
Use the buffer cache advisory over a given workload and then query the v$db_cache_advice table. If a change was necessary then I would use the alter system set db_cache_size command.

Explain an ORA-01555
You get this error when you get a snapshot too old within rollback. It can usually be solved by increasing the undo retention or increasing the size of rollbacks. You should also look at the logic involved in the application getting the error message.

Explain the difference between $ORACLE_HOME and $ORACLE_BASE.
ORACLE_BASE is the root directory for oracle. ORACLE_HOME located beneath ORACLE_BASE is where the oracle products reside.

How would you determine the time zone under which a database was operating?
select DBTIMEZONE from dual;

Explain the use of setting GLOBAL_NAMES equal to TRUE.
Setting GLOBAL_NAMES dictates how you might connect to a database. This variable is either TRUE or FALSE and if it is set to TRUE it enforces database links to have the same name as the remote database to which they are linking.

What command would you use to encrypt a PL/SQL application?
WRAP

Explain the difference between a FUNCTION, PROCEDURE and PACKAGE.
A function and procedure are the same in that they are intended to be a collection of PL/SQL code that carries a single task. While a procedure does not have to return any values to the calling application, a function will return a single value. A package on the other hand is a collection of functions and procedures that are grouped together based on their commonality to a business function or application.

Explain the use of table functions.
Table functions are designed to return a set of rows through PL/SQL logic but are intended to be used as a normal table or view in a SQL statement. They are also used to pipeline information in an ETL process.

Name three advisory statistics you can collect.
Buffer Cache Advice, Segment Level Statistics, & Timed Statistics

Where in the Oracle directory tree structure are audit traces placed?
In unix $ORACLE_HOME/rdbms/audit, in Windows the event viewer

Explain materialized views and how they are used.
Materialized views are objects that are reduced sets of information that have been summarized, grouped, or aggregated from base tables. They are typically used in data warehouse or decision support systems.

When a user process fails, what background process cleans up after it?
PMON

What background process refreshes materialized views?
The Job Queue Processes.

How would you determine what sessions are connected and what resources they are waiting for?
Use of V$SESSION and V$SESSION_WAIT

Describe what redo logs are.
Redo logs are logical and physical structures that are designed to hold all the changes made to a database and are intended to aid in the recovery of a database.

How would you force a log switch?
ALTER SYSTEM SWITCH LOGFILE;

Give two methods you could use to determine what DDL changes have been made.
You could use Logminer or Streams

What does coalescing a tablespace do?
Coalescing is only valid for dictionary-managed tablespaces and de-fragments space by combining neighboring free extents into large single extents.

What is the difference between a TEMPORARY tablespace and a PERMANENT tablespace?
A temporary tablespace is used for temporary objects such as sort structures while permanent tablespaces are used to store those objects meant to be used as the true objects of the database.

Name a tablespace automatically created when you create a database.
The SYSTEM tablespace.

When creating a user, what permissions must you grant to allow them to connect to the database?
Grant the CONNECT to the user.

How do you add a data file to a tablespace
ALTER TABLESPACE ADD DATAFILE SIZE

How do you resize a data file?
ALTER DATABASE DATAFILE RESIZE ;

What view would you use to look at the size of a data file?
DBA_DATA_FILES

What view would you use to determine free space in a tablespace?
DBA_FREE_SPACE

How would you determine who has added a row to a table?
Turn on fine grain auditing for the table.

How can you rebuild an index?
ALTER INDEX REBUILD;

Explain what partitioning is and what its benefit is.
Partitioning is a method of taking large tables and indexes and splitting them into smaller, more manageable pieces.

You have just compiled a PL/SQL package but got errors, how would you view the errors?
SHOW ERRORS

How can you gather statistics on a table?
The ANALYZE command.

How can you enable a trace for a session?
Use the DBMS_SESSION.SET_SQL_TRACE or
Use ALTER SESSION SET SQL_TRACE = TRUE;

What is the difference between the SQL*Loader and IMPORT utilities?
These two Oracle utilities are used for loading data into the database. The difference is that the import utility relies on the data being produced by another Oracle utility EXPORT while the SQL*Loader utility allows data to be loaded that has been produced by other utilities from different data sources just so long as it conforms to ASCII formatted or delimited files.

Name two files used for network connection to a database.
TNSNAMES.ORA and SQLNET.ORA

What is the function of Optimizer ?
The goal of the optimizer is to choose the most efficient way to execute a SQL statement.

What is Execution Plan ?
The combinations of the steps the optimizer chooses to execute a statement is called an execution plan.

Can one resize tablespaces and data files? (for DBA)
One can manually increase or decrease the size of a datafile from Oracle 7.2 using the command.
ALTER DATABASE DATAFILE 'filename2' RESIZE 100M;
Because you can change the sizes of datafiles, you can add more space to your database without adding more datafiles. This is beneficial if you are concerned about reaching the maximum number of datafiles allowed in your database.
Manually reducing the sizes of datafiles allows you to reclaim unused space in the database. This is useful for correcting errors in estimations of space requirements.
Also, datafiles can be allowed to automatically extend if more space is required. Look at the following command:
CREATE TABLESPACE pcs_data_ts
DATAFILE 'c:\ora_apps\pcs\pcsdata1.dbf' SIZE 3M
AUTOEXTEND ON NEXT 1M MAXSIZE UNLIMITED
DEFAULT STORAGE (INITIAL 10240
NEXT 10240
MINEXTENTS 1
MAXEXTENTS UNLIMITED
PCTINCREASE 0)
ONLINE
PERMANENT;

What is SAVE POINT ?
For long transactions that contain many SQL statements, intermediate markers or savepoints can be declared which can be used to divide a transaction into smaller parts. This allows the option of later rolling back all work performed from the current point in the transaction to a declared savepoint within the transaction.

What are the values that can be specified for OPTIMIZER MODE Parameter ?
COST and RULE.

Can one rename a tablespace? (for DBA)
No, this is listed as Enhancement Request 148742. Workaround:
Export all of the objects from the tablespace
Drop the tablespace including contents
Recreate the tablespace
Import the objects

What is RULE-based approach to optimization ?
Choosing an executing planbased on the access paths available and the ranks of these access paths.

What are the values that can be specified for OPTIMIZER_GOAL parameter of the ALTER SESSION Command ?
CHOOSE,ALL_ROWS,FIRST_ROWS and RULE.

How does one create a standby database? (for DBA)
While your production database is running, take an (image copy) backup and restore it on duplicate hardware. Note that an export will not work!!!
On your standby database, issue the following commands:
ALTER DATABASE CREATE STANDBY CONTROLFILE AS 'filename';
ALTER DATABASE MOUNT STANDBY DATABASE;
RECOVER STANDBY DATABASE;
On systems prior to Oracle 8i, write a job to copy archived redo log files from the primary database to the standby system, and apply the redo log files to the standby database (pipe it). Remember the database is recovering and will prompt you for the next log file to apply.
Oracle 8i onwards provide an "Automated Standby Database" feature, which will send archived, log files to the remote site via NET8, and apply then to the standby database.
When one needs to activate the standby database, stop the recovery process and activate it:
ALTER DATABASE ACTIVATE STANDBY DATABASE;

How does one give developers access to trace files (required as input to tkprof)? (for DBA)
The "alter session set sql_trace=true" command generates trace files in USER_DUMP_DEST that can be used by developers as input to tkprof. On Unix the default file mask for these files are "rwx r-- ---".
There is an undocumented INIT.ORA parameter that will allow everyone to read (rwx r-r--) these trace files:
_trace_files_public = true
Include this in your INIT.ORA file and bounce your database for it to take effect.

What are the responsibilities of a Database Administrator ?
Installing and upgrading the Oracle Server and application tools. Allocating system storage and planning future storage requirements for the database system. Managing primary database structures (tablespaces) Managing primary objects (table,views,indexes) Enrolling users and maintaining system security. Ensuring compliance with Oralce license agreement Controlling and monitoring user access to the database. Monitoring and optimizing the performance of the database. Planning for backup and recovery of database information. Maintain archived data on tape Backing up and restoring the database. Contacting Oracle Corporation for technical support.

What is a trace file and how is it created ?
Each server and background process can write an associated trace file. When an internal error is detected by a process or user process, it dumps information about the error to its trace. This can be used for tuning the database.

What are the roles and user accounts created automatically with the database?
DBA - role Contains all database system privileges.
SYS user account - The DBA role will be assigned to this account. All of the base tables and views for the database's dictionary are store in this schema and are manipulated only by ORACLE. SYSTEM user account - It has all the system privileges for the database and additional tables and views that display administrative information and internal tables and views used by oracle tools are created using this username.

What are the minimum parameters should exist in the parameter file (init.ora) ?
DB NAME - Must set to a text string of no more than 8 characters and it will be stored inside the datafiles, redo log files and control files and control file while database creation.
DB_DOMAIN - It is string that specifies the network domain where the database is created. The global database name is identified by setting these parameters
(DB_NAME & DB_DOMAIN) CONTORL FILES - List of control filenames of the database. If name is not mentioned then default name will be used.
DB_BLOCK_BUFFERS - To determine the no of buffers in the buffer cache in SGA.
PROCESSES - To determine number of operating system processes that can be connected to ORACLE concurrently. The value should be 5 (background process) and additional 1 for each user.
ROLLBACK_SEGMENTS - List of rollback segments an ORACLE instance acquires at database startup. Also optionally LICENSE_MAX_SESSIONS,LICENSE_SESSION_WARNING and LICENSE_MAX_USERS.

Why and when should I backup my database? (for DBA)
Backup and recovery is one of the most important aspects of a DBAs job. If you lose your company's data, you could very well lose your job. Hardware and software can always be replaced, but your data may be irreplaceable!
Normally one would schedule a hierarchy of daily, weekly and monthly backups, however consult with your users before deciding on a backup schedule. Backup frequency normally depends on the following factors:
. Rate of data change/ transaction rate
. Database availability/ Can you shutdown for cold backups?
. Criticality of the data/ Value of the data to the company
. Read-only tablespace needs backing up just once right after you make it read-only
. If you are running in archivelog mode you can backup parts of a database over an extended cycle of days
. If archive logging is enabled one needs to backup archived log files timeously to prevent database freezes
. Etc.
Carefully plan backup retention periods. Ensure enough backup media (tapes) are available and that old backups are expired in-time to make media available for new backups. Off-site vaulting is also highly recommended.
Frequently test your ability to recover and document all possible scenarios. Remember, it's the little things that will get you. Most failed recoveries are a result of organizational errors and miscommunications.

What strategies are available for backing-up an Oracle database? (for DBA)
The following methods are valid for backing-up an Oracle database:
Export/Import - Exports are "logical" database backups in that they extract logical definitions and data from the database to a file.
Cold or Off-line Backups - Shut the database down and backup up ALL data, log, and control files.
Hot or On-line Backups - If the databases are available and in ARCHIVELOG mode, set the tablespaces into backup mode and backup their files. Also remember to backup the control files and archived redo log files.
RMAN Backups - While the database is off-line or on-line, use the "rman" utility to backup the database.
It is advisable to use more than one of these methods to backup your database. For example, if you choose to do on-line database backups, also cover yourself by doing database exports. Also test ALL backup and recovery scenarios carefully. It is better to be save than sorry.
Regardless of your strategy, also remember to backup all required software libraries, parameter files, password files, etc. If your database is in ARCGIVELOG mode, you also need to backup archived log files.

What is the difference between online and offline backups? (for DBA)
A hot backup is a backup performed while the database is online and available for read/write. Except for Oracle exports, one can only do on-line backups when running in ARCHIVELOG mode.
A cold backup is a backup performed while the database is off-line and unavailable to its users.

What is the difference between restoring and recovering? (for DBA)
Restoring involves copying backup files from secondary storage (backup media) to disk. This can be done to replace damaged files or to copy/move a database to a new location.
Recovery is the process of applying redo logs to the database to roll it forward. One can roll-forward until a specific point-in-time (before the disaster occurred), or roll-forward until the last transaction recorded in the log files. Sql> connect SYS as SYSDBA
Sql> RECOVER DATABASE UNTIL TIME '2001-03-06:16:00:00' USING BACKUP CONTROLFILE;

How does one backup a database using the export utility? (for DBA)
Oracle exports are "logical" database backups (not physical) as they extract data and logical definitions from the database into a file. Other backup strategies normally back-up the physical data files.
One of the advantages of exports is that one can selectively re-import tables, however one cannot roll-forward from an restored export file. To completely restore a database from an export file one practically needs to recreate the entire database.
Always do full system level exports (FULL=YES). Full exports include more information about the database in the export file than user level exports.

What are the built_ins used the display the LOV?
Show_lov
List_values

How do you call other Oracle Products from Oracle Forms?
Run_product is a built-in, Used to invoke one of the supported oracle tools products and specifies the name of the document or module to be run. If the called product is unavailable at the time of the call, Oracle Forms returns a message to the operator.

What is the main diff. bet. Reports 2.0 & Reports 2.5?
Report 2.5 is object oriented.

What are the Built-ins to display the user-named editor?
A user named editor can be displayed programmatically with the built in procedure SHOW-EDITOR, EDIT_TETITEM independent of any particular text item.

How many number of columns a record group can have?
A record group can have an unlimited number of columns of type CHAR, LONG, NUMBER, or DATE provided that the total number of column does not exceed 64K.

What is a Query Record Group?
A query record group is a record group that has an associated SELECT statement. The columns in a query record group derive their default names, data types, had lengths from the database columns referenced in the SELECT statement. The records in query record group are the rows retrieved by the query associated with that record group. What is a Non Query Record Group?

What does the term panel refer to with regard to pages?
A panel is the no. of physical pages needed to print one logical page.

What is a master detail relationship?
A master detail relationship is an association between two base table blocks- a master block and a detail block. The relationship between the blocks reflects a primary key to foreign key relationship between the tables on which the blocks are based.

What is a library?
A library is a collection of subprograms including user named procedures, functions and packages.

What is an anchoring object & what is its use? What are the various sub events a mouse double click event involves?
An anchoring object is a print condition object which used to explicitly or implicitly anchor other objects to itself.

Use the add_group_column function to add a column to record group that was created at a design time?
False

What are the various sub events a mouse double click event involves? What are the various sub events a mouse double click event involves?
Double clicking the mouse consists of the mouse down, mouse up, mouse click, mouse down & mouse up events.

What is the use of break group? What are the various sub events a mouse double click event involves?
A break group is used to display one record for one group ones. While multiple related records in other group can be displayed.

What tuning indicators can one use? (for DBA)
The following high-level tuning indicators can be used to establish if a database is performing optimally or not:
. Buffer Cache Hit Ratio
Formula: Hit Ratio = (Logical Reads - Physical Reads) / Logical Reads
Action: Increase DB_CACHE_SIZE (DB_BLOCK_BUFFERS prior to 9i) to increase hit ratio
. Library Cache Hit Ratio
Action: Increase the SHARED_POOL_SIZE to increase hit ratio

What tools/utilities does Oracle provide to assist with performance tuning? (for DBA)
Oracle provide the following tools/ utilities to assist with performance monitoring and tuning:
. TKProf
. UTLBSTAT.SQL and UTLESTAT.SQL - Begin and end stats monitoring
. Statspack
. Oracle Enterprise Manager - Tuning Pack

What is STATSPACK and how does one use it? (for DBA)
Statspack is a set of performance monitoring and reporting utilities provided by Oracle from Oracle8i and above. Statspack provides improved BSTAT/ESTAT functionality, though the old BSTAT/ESTAT scripts are still available. For more information about STATSPACK, read the documentation in file $ORACLE_HOME/rdbms/admin/spdoc.txt.
Install Statspack:
cd $ORACLE_HOME/rdbms/admin
sqlplus "/ as sysdba" @spdrop.sql -- Install Statspack -
sqlplus "/ as sysdba" @spcreate.sql-- Enter tablespace names when prompted
Use Statspack:
sqlplus perfstat/perfstat
exec statspack.snap; -- Take a performance snapshots
exec statspack.snap;
o Get a list of snapshots
select SNAP_ID, SNAP_TIME from STATS$SNAPSHOT;
@spreport.sql -- Enter two snapshot id's for difference report
Other Statspack Scripts:
. sppurge.sql - Purge a range of Snapshot Id's between the specified begin and end Snap Id's
. spauto.sql - Schedule a dbms_job to automate the collection of STATPACK statistics
. spcreate.sql - Installs the STATSPACK user, tables and package on a database (Run as SYS).
. spdrop.sql - Deinstall STATSPACK from database (Run as SYS)
. sppurge.sql - Delete a range of Snapshot Id's from the database
. spreport.sql - Report on differences between values recorded in two snapshots
. sptrunc.sql - Truncates all data in Statspack tables

What are the common RMAN errors (with solutions)? (for DBA)
Some of the common RMAN errors are:
RMAN-20242: Specification does not match any archivelog in the recovery catalog.
Add to RMAN script: sql 'alter system archive log current';
RMAN-06089: archived log xyz not found or out of sync with catalog
Execute from RMAN: change archivelog all validate;

How can you execute the user defined triggers in forms 3.0 ?
Execute Trigger (trigger-name)

What ERASE package procedure does ?
Erase removes an indicated global variable.

What is the difference between NAME_IN and COPY ?
Copy is package procedure and writes values into a field.
Name in is a package function and returns the contents of the variable to which you apply.

What package procedure is used for calling another form ?
Call (E.g. Call(formname)

When the form is running in DEBUG mode, If you want to examine the values of global variables and other form variables, What package procedure command you would use in your trigger text ?
Break.
SYSTEM VARIABLES

The value recorded in system.last_record variable is of type
a. Number
b. Boolean
c. Character. ?
b. Boolean.

What is mean by Program Global Area (PGA) ?
It is area in memory that is used by a Single Oracle User Process.

What is hit ratio ?
It is a measure of well the data cache buffer is handling requests for data. Hit Ratio = (Logical Reads - Physical Reads - Hits Misses)/ Logical Reads.

How do u implement the If statement in the Select Statement
We can implement the if statement in the select statement by using the Decode statement. e.g. select DECODE (EMP_CAT,'1','First','2','Second'Null); Here the Null is the else statement where null is done .

How many types of Exceptions are there
There are 2 types of exceptions. They are
a) System Exceptions
e.g. When no_data_found, When too_many_rows
b) User Defined Exceptions
e.g. My_exception exception
When My_exception then

What are the inline and the precompiler directives
The inline and precompiler directives detect the values directly

How do you use the same lov for 2 columns
We can use the same lov for 2 columns by passing the return values in global values and using the global values in the code

How many minimum groups are required for a matrix report
The minimum number of groups in matrix report are 4

What is the difference between static and dynamic lov
The static lov contains the predetermined values while the dynamic lov contains values that come at run time

How does one manage Oracle database users? (for DBA)
Oracle user accounts can be locked, unlocked, forced to choose new passwords, etc. For example, all accounts except SYS and SYSTEM will be locked after creating an Oracle9iDB database using the DB Configuration Assistant (dbca). DBA's must unlock these accounts to make them available to users.
Look at these examples:
ALTER USER scott ACCOUNT LOCK -- lock a user account
ALTER USER scott ACCOUNT UNLOCK; -- unlocks a locked users account
ALTER USER scott PASSWORD EXPIRE; -- Force user to choose a new password

What is the difference between DBFile Sequential and Scattered Reads?(for DBA)
Both "db file sequential read" and "db file scattered read" events signify time waited for I/O read requests to complete. Time is reported in 100's of a second for Oracle 8i releases and below, and 1000's of a second for Oracle 9i and above. Most people confuse these events with each other as they think of how data is read from disk. Instead they should think of how data is read into the SGA buffer cache.
db file sequential read:
A sequential read operation reads data into contiguous memory (usually a single-block read with p3=1, but can be multiple blocks). Single block I/Os are usually the result of using indexes. This event is also used for rebuilding the control file and reading data file headers (P2=1). In general, this event is indicative of disk contention on index reads.
db file scattered read:
Similar to db file sequential reads, except that the session is reading multiple data blocks and scatters them into different discontinuous buffers in the SGA. This statistic is NORMALLY indicating disk contention on full table scans. Rarely, data from full table scans could be fitted into a contiguous buffer area, these waits would then show up as sequential reads instead of scattered reads.
The following query shows average wait time for sequential versus scattered reads:
prompt "AVERAGE WAIT TIME FOR READ REQUESTS"
select a.average_wait "SEQ READ", b.average_wait "SCAT READ"
from sys.v_$system_event a, sys.v_$system_event b
where a.event = 'db file sequential read'
and b.event = 'db file scattered read';

What is the use of PARFILE option in EXP command ?
Name of the parameter file to be passed for export.

What is the use of TABLES option in EXP command ?
List of tables should be exported.ze)

What is the OPTIMAL parameter?
It is used to set the optimal length of a rollback segment.

How does one use ORADEBUG from Server Manager/ SQL*Plus? (for DBA)
Execute the "ORADEBUG HELP" command from svrmgrl or sqlplus to obtain a list of valid ORADEBUG commands. Look at these examples:
SQLPLUS> REM Trace SQL statements with bind variables
SQLPLUS> oradebug setospid 10121
Oracle pid: 91, Unix process pid: 10121, image: oracleorcl
SQLPLUS> oradebug EVENT 10046 trace name context forever, level 12
Statement processed.
SQLPLUS> ! vi /app/oracle/admin/orcl/bdump/ora_10121.trc
SQLPLUS> REM Trace Process Statistics
SQLPLUS> oradebug setorapid 2
Unix process pid: 1436, image: ora_pmon_orcl
SQLPLUS> oradebug procstat
Statement processed.
SQLPLUS>> oradebug TRACEFILE_NAME
/app/oracle/admin/orcl/bdump/pmon_1436.trc
SQLPLUS> REM List semaphores and shared memory segments in use
SQLPLUS> oradebug ipc
SQLPLUS> REM Dump Error Stack
SQLPLUS> oradebug setospid
SQLPLUS> oradebug event immediate trace name errorstack level 3
SQLPLUS> REM Dump Parallel Server DLM locks
SQLPLUS> oradebug lkdebug -a convlock
SQLPLUS> oradebug lkdebug -a convres
SQLPLUS> oradebug lkdebug -r (i.e 0x8066d338 from convres dump)

Are there any undocumented commands in Oracle? (for DBA)
Sure there are, but it is hard to find them. Look at these examples:
From Server Manager (Oracle7.3 and above): ORADEBUG HELP
It looks like one can change memory locations with the ORADEBUG POKE command. Anyone brave enough to test this one for us? Previously this functionality was available with ORADBX (ls -l $ORACLE_HOME/rdbms/lib/oradbx.o; make -f oracle.mk oradbx) SQL*Plus: ALTER SESSION SET CURRENT_SCHEMA = SYS