Tuesday, April 12, 2011

Oracle Reports Interview Questions & Answers Part 1

racle Reports - Technical Interview Questions & Answers

How many different triggers are available in Report?

There are five types of triggers in report 6i
1) Before report trigger
2) After report trigger
3) Before Parameter trigger
4) After parameter trigger
5) Between pages trigger

What is the Firing sequence of report trigger?
First the before parameter trigger will raise, after firing this trigger parameter form will displayed,

after passing parameter after parameter trigger will fire query will parsed &

then before report trigger will fired then if there are number of pages in your report

then the between pages trigger will fired but it will fire between first & second & so on pages but it will not fired in reverse condition the after report trigger will fire

after closing the run time parameter form is closed.

What is the difference between After Parameter Trigger and Before Report Trigger? 

After parameter Trigger: It will fire after the parameter form is displayed.here we can do validation on parameter values
Before Report Trigger: It will fire before the report is executed and after the query is parsed and date is fetched.

What is the Format Trigger?
Format Trigger is a PL/SQL function. This trigger is going to fire before an object is printed in report output. it return boolean-true then go to print -false then don't print.

What is the diff. when Flex mode is mode on and when it is off?
When flex mode is on, reports automatically resizes the parent when the child is resized.

What is the diff. when confine mode is on and when it is off?
When confine mode is on, an object cannot be moved outside its parent in the layout.

What is a lexical parameter?
Lexical Parameter is used to replace the where, order by conditions at run time.

What are bind variables?
Bind variables are used in report 6i for replacing the single parameter in the select statement

How many different layouts are available in Reports?
There are eight different layout formats:
1. Tabular
2. Form Like
3. Form Letter
4. Mailing Label
5. Group Left
6. Group Above
7. Matrix
8. Matrix with group

What is the minimum number of groups required for a matrix report?
The minimum of groups required for a matrix report are 4

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 the Anchoring in Reports?
Anchor is used to make fixed distance between two objects in Reports Layout.

What is the difference between Frame and Repeating Frame?
Frames are used to surround other objects and protect them from being overwritten or pushed by other objects. For example a frame might be used to surround all objects owned by a group to surround column headings or to surround summaries.

When you default the layout for a report Report Builder creates frames around report objects as needed; you can also create a frame manually in the Layout Model view.

Repeating frames surround all of the fields that are created for a group’s columns. The repeating frame prints (is fired) once for each record of the group.
When you default the layout for a report Report Builder creates repeating frames around fields as needed; you can also create a repeating frame manually in the Layout Model view

What are different types of column in reports?
There are three types of columns in the report 6i these are:
1) Placeholder Column – Placeholder column is used to store a value for a variable.
2) Formula Column
3) Summary Column

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. Yes it is possible to run the report without parameter form by setting the PARAM value to Null

Oracle Forms Interview Questions & Answers Part 2

What are the vbx controls?
Vbx control provide a simple method of building and enhancing user interfaces. The controls can use to obtain user inputs and display program outputs.vbx control where originally develop as extensions for the ms visual basic environments and include such items as sliders, rides and knobs.

What is the "LOV of Validation" Property of an item? What is the use of it?

When LOV for Validation is set to True, Oracle Forms compares the current value of the text item to the values in the first column displayed in the LOV. Whenever the validation event occurs. If the value in the text item matches one of the values in the first column of the LOV, validation succeeds, the LOV is not displayed, and processing continues normally. If the value in the text item does not match one of the values in the first column of the LOV, Oracle Forms displays the LOV and uses the text item value as the search criteria to automatically reduce the list.

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

What are the difference between lov & list item?
Lov is a property where as list item is an item. A list item can have only one column, lov can have one or more columns

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

What are the different types of Record Groups?
Query Record Groups
NonQuery Record Groups
State Record Groups

What are the different display styles of list items?
Combo box

Can on bypass the Oracle login screen?
The first thing that the user sees when using runform is the Oracle logon prompt asking them for their username, password, and database to connect to. You can bypass this screen or customise it by displaying your own logon screen.


ON-LOGIN  Form-Level Trigger

uname varchar2(10);
pass varchar2(10);
con_string varchar2(30);

uname := 'scott';
pass :='tiger';

logon(uname, pass||'@'||con_string);

What are parameters?
Parameters provide a simple mechanism for defining and setting the valuesof inputs that are required by a form at startup. Form parameters are variables of type char,number,date that you define at design time.

What are difference between post database commit and post-form commit?
Post-form commit fires once during the post and commit transactions process, after the database commit occurs. The post-form-commit trigger fires after inserts, updates and deletes have been posted to the database but before the transactions have been finalized in the issuing the command. The post-database-commit trigger fires after oracle forms issues the commit to finalized transactions.

Can one Maximize/ Minimize a Window in Forms?
On MS-Windows, Forms run inside a Windows Multiple-Document Interface (MDI) window. You can use SET_WINDOW_PROPERTY on the window called FORMS_MDI_WINDOW to resize this MDI (or any other named) window. Examples:
set_window_property(FORMS_MDI_WINDOW, POSITION, 7, 15);
set_window_property('my_window_name', WINDOW_STATE, MAXIMIZE);

What are the different modals of windows?
Modalless windows
Modal windows

What are modal windows?
Modal windows are usually used as dialogs, and have restricted functionality compared to modelless windows. On some platforms for example operators cannot resize, scroll or iconify a modal window.


What is Raise_application_error ?

Raise_application_error is a procedure of package DBMS_STANDARD which allows to
issue an user_defined error messages from stored sub-program or database trigger.

What are the return values of functions SQLCODE and SQLERRM ?
SQLCODE returns the latest code of the error that has occured.
SQLERRM returns the relevant error message of the SQLCODE.

Where the Pre_defined_exceptions are stored ?

In the standard package.
Procedures, Functions & Packages ;

What is difference between a PROCEDURE & FUNCTION ?

A FUNCTION is always returns a value using the return statement.
A PROCEDURE may return one or more values through parameters or may not
Return at all.

What are advantages of Stored Procedures?

Extensibility, Modularity, Reusability, Maintainability and one time compilation.

What are the modes of parameters that can be passed to a procedure ?

IN,OUT,IN-OUT parameters.

What are the two parts of a Pakage?
Pakage Specification and Pakage Body.

Give the structure of the procedure ?

PROCEDURE name (parameter list.....)
local variable declarations
Executable statements.
exception handlers

Give the structure of the function ?
FUNCTION name (argument list .....) Return datatype is
local variable declarations
executable statements
execution handlers

Explain how procedures and functions are called in a PL/SQL block ?

Function is called as part of an expression.
sal := calculate_sal ('a822');
procedure is called as a PL/SQL statement
calculate_bonus ('A822');
26. What is Overloading of procedures ?
The Same procedure name is repeated with parameters of different datatypes and
parameters in different positions, varying number of parameters is called overloading of

e.g. DBMS_OUTPUT put_line

What is a package ? What are the advantages of packages ?

Package is a database object that groups logically related procedures.
The advantages of packages are Modularity, Easier Applicaton Design, Information.
Hiding,. reusability and Better Performance.

What are two parts of package ?

The two parts of package are PACKAGE SPECIFICATION & PACKAGE BODY.

Package Specification contains declarations that are global to the packages and local to the schema.
Package Body contains actual procedures and local declaration of the procedures and cursor declarations.

What is difference between a Cursor declared in a procedure and Cursor
declared in a package specification ?

A cursor declared in a package specification is global and can be accessed by other
procedures or procedures in a package.
A cursor declared in a procedure is local to the procedure that can not be accessed by
other procedures.
30. Name the tables where characteristics of Package, procedure and functions are stored ?
User_objects, User_Source and User_error.

What is an Exception ? What are types of Exception ?

Exception is the error handling part of PL/SQL block. The types are Predefined and
user_defined. Some of Predefined execptions are.



What is PL/SQL ?

PL/SQL is a procedural language that has both interactive SQL and procedural
programming language constructs such as iteration, conditional branching.

What is the basic structure of PL/SQL ?

PL/SQL uses block structure as its basic structure. Anonymous blocks or nested blocks
can be used in PL/SQL.

Declarative part, Executable part and Execption part.


What are the datatypes a available in PL/SQL ?

Some scalar data types such as
Some composite data types such as RECORD & TABLE.

 What are % TYPE and % ROWTYPE ? What are the advantages of using these over datatypes?

% TYPE provides the data type of a variable or a database column to that variable.

% ROWTYPE provides the record type that represents a entire row of a table or view or
columns selected in the cursor.

The advantages:
i. Need not know about variable's data type
ii. If the database definition of a column in a table changes, the data type of a variable
changes accordingly.

What is difference between % ROWTYPE and TYPE RECORD ?

% ROWTYPE is to be used whenever query returns a entire row of a table or view.
TYPE rec RECORD is to be used whenever query returns columns of different table or views and variables.

E.g. TYPE r_emp is RECORD (eno emp.empno% type,ename emp ename %type );
e_rec emp% ROWTYPE
cursor c1 is select empno,deptno from emp;
e_rec c1 %ROWTYPE.

What is PL/SQL table ?

Objects of type TABLE are called "PL/SQL tables", which are modelled as (but not the same as) database tables, PL/SQL tables use a primary PL/SQL tables can have one column and a primary key.

What is a cursor ? Why Cursor is required ?
Cursor is a named private SQL area from where information can be accessed.
Cursors are required to process rows individually for queries returning multiple rows.

Explain the two type of Cursors ?

There are two types of cursors, Implict Cursor and Explicit Cursor.
PL/SQL uses Implict Cursors for queries.
User defined cursors are called Explicit Cursors. They can be declared and used.

What are the PL/SQL Statements used in cursor processing ?

DECLARE CURSOR cursor name, OPEN cursor name, FETCH cursor name INTO or Record types, CLOSE cursor name.

What are the cursor attributes used in PL/SQL ?

%ISOPEN - to check whether cursor is open or not
% ROWCOUNT - number of rows featched/updated/deleted.
% FOUND - to check whether cursor has fetched any row. True if rows are featched.
% NOT FOUND - to check whether cursor has featched any row. True if no rows are featched.
These attributes are proceded with SQL for Implict Cursors and with Cursor name for Explict Cursors.

What is a cursor for loop ?

Cursor for loop implicitly declares %ROWTYPE as loop index,opens a cursor, fetches
rows of values from active set into fields in the record and closes when all the records have
been processed.

eg. FOR emp_rec IN C1 LOOP
salary_total := salary_total +emp_rec sal;

Explain the usage of WHERE CURRENT OF clause in cursors ?

WHERE CURRENT OF clause in an UPDATE,DELETE statement refers to the latest
row fetched from a cursor.

What is Pragma EXECPTION_INIT ? Explain the usage ?
The PRAGMA EXECPTION_INIT tells the complier to associate an exception with an
oracle error. To get an error message of a specific oracle error.

e.g. PRAGMA EXCEPTION_INIT (exception name, oracle error number)

Useful Scripts Collection Part 1

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SCRIPT COLLECTION - How-to find global name of your database?
ora9i$maran> select * from global_name;


find Primary key constraints for a given table name?
ora9i$maran> Select
3 from
4 USER_CONS_COLUMNS C ,user_constraints T
5 where
9 c.table_name = '&TNAM'
10 /
Enter value for tnam: RIGHTS
SYS_C001420 RIGHTS &n bsp; RIGHTS_ID

find available indexes for a given table name?
ora9i$maran> select table_name||' - '|| COLUMN_NAME||' - '|| INDEX_NAME
2 from user_ind_columns where table_name like UPPER('%&TN%')
3 /
------------------------------------------------- -------

find Primary key and Unique key for a given table?
7 A.CONSTRAINT_TYPE in ('U','P') and
8 A.TABLE_NAME LIKE upper('%&tn')
9 /
Enter value for tn: ROLE
old 8: A.TABLE_NAME LIKE upper('%&tn')
new 8: A.TABLE_NAME LIKE upper('%ROLE')
-------------- ------------------------------------------------------------------

find the object created date?
ora9iAS$maran@TIFA> select OBJECT_NAME||' - '||OBJECT_TYPE||' - '||CREATED from
2 user_objects where OBJECT_NAME like upper('%&objname%')
3 /
Enter value for objname: COUNTER_MAS$
old 2: user_objects where OBJECT_NAME like upper('%&objname%')
new 2: user_objects where OBJECT_NAME like upper('%COUNTER%')

find all schemas and its created date?
ora9iAS$maran@TIFA> select username,CREATED from all_users order by 2,1;
------------------------------ ---------
SYS 23-NOV-04
TIFA 23-NOV-04
find reference tables of a given primary table?

ora9iAS$maran@TIFA> Select c.TABLE_NAME FTN
2 from
3 USER_CONS_COLUMNS C ,user_constraints T
4 where
9 USER_CONS_COLUMNS C ,user_constraints T
10 where
14 c.table_name = '&TNAM')
15 /
Enter value for tnam: COUNTER_MAS$'
old 14: c.table_name = '&TNAM')
new 14: c.table_name = 'COUNTER_MAS$')

find server ip address?
ora9iAS$maran@TIFA> SELECT UTL_INADDR.get_host_address from dual;
------------------------------------------------------------------------------ --

find last number of a given sequence?
ora9iAS$maran@TIFA> select SEQUENCE_NAME, LAST_NUMBER from user_sequences where upper(SEQUENCE_NAME) like upper('%&sn%');
Enter value for sn: BANK
old 2: where upper(SEQUENCE_NAME) like upper('%&sn%')
new 2: where upper(SEQUENCE_NAME) like upper('%BANK%')
------------------------------ -----------

SQL*Loader is a bulk loader utility used for moving data from external files into the Oracle database. SQL*Loader supports various load formats, selective loading, and multi-table loads.
Can I load more than one input file at the same time?
INFILE 'C:empcsv1.csv'
INFILE 'C:empcsv2.csv'
INFILE 'C:empcsv3.csv'

You need to DBA privilege to run the following queries:

find out the objects created in SYSTEM tablespace other than SYSTEM, SYS users?
ora9i$maran> SELECT TABLE_NAME, OWNER from dba_tables
2 rows selected.

find size of the database?
ora9i$maran> select sum(bytes)/1024/1024 "Total DB size in Meg" from sys.v_$datafile;
Total DB size in Meg

find segment size greater then 1 MB?
ora9i$maran> select OWNER||' - '||SEGMENT_NAME||' - '||(BYTES/1024)/1024||' MB'
2 from dba_segments where (BYTES/1024)/1024 >=1 AND
3 OWNER like UPPER('%&OWNER%')
4 /
Enter value for owner: UCB
---------------------------------------- ------------------------------------------
UCB - TERM1_DB - 6.515625 MB
UCB - TERM1_XL - 6.4609375 MB

find all schema size?
ora9i$maran> select owner , sum(bytes/1024/1024) MB
2 from dba_segments
3 group by owner order by 2
4 /
KENT .0625
SYSTEM 3.34375
VIP 57.96875
CVB 263.25
ER_CVB 344.460938
SYS 391.492188

find users those who have DBA privilege?
ora9i$maran> select grantee "DBA Privilege"
2 from dba_role_privs
3 where granted_role='DBA';
DBA Privilege

move objects from current tablespace to another
REM create a file name with movetsall.sql using this content
column movets new_value movets noprint
select 'c:'||'Move_Tablespace_Script_'||USER||'_'||to_char(sysdate,'DDMMYYYY')||'.SQL' movets from DUAL;
spool && movets
select decode( segment_type, 'TABLE',
segment_name, table_name ) order_col1,
decode( segment_type, 'TABLE', 1, 2 ) order_col2,
'alter ' || LOWER(segment_type) || ' ' || segment_name ||chr(10) ||
decode( segment_type, 'TABLE', ' move ', ' rebuild ' ) ||
' tablespace &Taget_Tablespace_Name ' ||chr(10) ||
' storage '||chr(10) ||
' ('||chr(10) ||
' initial ' || initial_extent || ' next ' ||next_extent ||chr(10) ||
' minextents ' || min_extents || ' maxextents ' ||max_extents ||chr(10) ||
' pctincrease ' || pct_increase || ' freelists ' ||
freelists ||chr(10) ||
' );'
from user_segments,
(select table_name, index_name from user_indexes )
where segment_type in ( 'TABLE', 'INDEX' )
and segment_name = index_name (+)
order by 1, 2
REM edit 'c:Move_Tablespace_Script__.SQL’, modify as needed and run it.

DBA (Basic) Part 2

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.

What does a Control file Contain ?
A Control file records the physical structure of the database. It contains the following information.

i. Database Name
ii. Names and locations of a database's files and redolog files.
iii. Time stamp of database creation.

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 the prevents database data from being written to a database's data files.

What is a Data Dictionary ?

The data dictionary of an ORACLE database is a set of tables and views that are used a read-only reference about the database.

It stores information about both the logical and physical structure of the database, the valid users of an ORACLE database, integrity constraints defined for tables in the database and space allocated for a schema object and how much of it is being used.

What is Two-Phase Commit ?
Two-phase commit is mechanism that guarantees a distributed transaction either commits on all involved nodes or rolls back on all involved nodes to maintain data consistency across the global distributed database. It has two phase, a Prepare Phase and a Commit Phase.

Describe two phases of Two-phase commit ?
Prepare phase - The global coordinator (initiating node) ask a participants to prepare (to promise to commit or rollback the transaction, even if there is a failure)

Commit - Phase - If all participants respond to the coordinator that they are prepared, the coordinator asks all nodes to commit the transaction, if all participants cannot prepare, the coordinator asks all nodes to roll back the transaction.

What is the mechanism provided by ORACLE for table replication ?
Snapshots and SNAPSHOT LOGs

What is a SQL * NET?
SQL *NET is ORACLE's mechanism for interfacing with the communication protocols used by the networks that facilitate distributed processing and distributed databases. It is used in Clint-Server and Server-Server communications.

What is the use of ANALYZE command ?
To perform one of these function on an index,table, or cluster:

- to collect statisties about object used by the optimizer and store them in the data
- to delete statistics about the object used by object from the data dictionary.
- to validate the structure of the object.
- to identify migrated and chained rows of the table or cluster.

What are the benefits of distributed options in databases ?
Database on other servers can be updated and those transactions can be grouped together with others in a logical unit.
Database uses a two phase commit.

What is the use of COMPRESS option in EXP command ?
Flag to indicate whether export should compress fragmented segments into single extents.

What is the use of GRANT option in EXP command ?
A flag to indicate whether grants on databse objects will be exported or not. Value is 'Y' or

What is the use of INDEXES option in EXP command ?
A flag to indicate whether indexes on tables will be exported.

What is the use of ROWS option in EXP command ?
Flag to indicate whether table rows should be exported. If 'N' only DDL statements for the
databse objects will be created.

What is the use of CONSTRAINTS option in EXP command ?
A flag to indicate whether constraints on table need to be exported.

What is the use of FULL option in EXP command ?
A flag to indicate whether full databse export should be performed.

What is the use of OWNER option in EXP command ?
List of table accounts should be exported.

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

What is the use of RECORD LENGTH option in EXP command ?
Record length in bytes.

What is the use of INCTYPE option in EXP command ?
Type export should be performed COMPLETE,CUMULATIVE,INCREMENTAL.

What is the use of RECORD option in EXP command ?
For Incremental exports, the flag indirects whether a record will be stores data dictionary
tables recording the export.

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 FILE option in IMP command ?
The name of the file from which import should be performed.

What is the use of IGNORE option in IMP command ?
A flag to indicate whether the import should ignore errors encounter when issuing CREATE

What is the use of GRANT option in IMP command ?
A flag to indicate whether grants on database objects will be imported.

What is the use of INDEXES option in IMP command ?
A flag to indicate whether import should import index on tables or not.

What is the use of ROWS option in IMP command ?
A flag to indicate whether rows should be imported. If this is set to 'N' then only DDL for database objects will be exectued.

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.

How can you rebuild an index?

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 formattsed or delimited files.

Name two files used for network connection to a database.


DBA (Basic) Part 1

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Level: Intermediate

What are the components of Physical database structure of Oracle Database?.
ORACLE database is comprised of three types of files. One or more Data files, two are more Redo Log files, and one or more Control files.

What are the components of Logical database structure of ORACLE database?
Tablespaces and the 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 Tablespace Quota ?
The collective amount of disk space available to the objects in a schema on a particular tablespace.

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.?

Can a Tablespace hold objects from different Schemes ?

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

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

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

What is a Public Synonyms ?
A Public synonyms can be accessed by any user on the database.

What are synonyms used for ?
Synonyms are used to : Mask the real name and owner of an object.
Provide public access to an object
Provide location transparency for tables,views or program units of a remote database.
Simplify the SQL statements for database users.

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.

How are Indexes Update ?
Indexes are automatically maintained and used by ORACLE. Changes to table data are automatically incorporated into all relevant indexes.

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

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 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 a Data File ?
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's redo log.

SQL*Plus and SQL - Part 2

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 TRUNCATE

DELETE allows the filtered deletion. Deleted records can be rolled back or committed.
Database triggers fire on DELETE.

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 retrive rows that do not have corresponding join value in the other table.

Difference between SUBSTR and INSTR ?

INSTR (String1,String2(n,(m)),
INSTR returns the position of the mth occurrence of the string 2 in string1. The search begins from nth position of string1.

SUBSTR (String1 n,m)
SUBSTR returns a character string of size m in string1, starting from nth postion of string1.


INTERSECT returns all distinct rows selected by both queries.
MINUS - returns all distinct rows selected by the first query but not by the second.
UNION - returns all distinct rows selected by either query
UNION ALL - returns all rows selected by either query,including all duplicates.

What is ROWID ?

ROWID is a pseudo column attached to each row of a table. It is 18 character long, blockno, rownumber are the components of ROWID.

What is the fastest way of accessing a row in a table ?

Using ROWID.

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.

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 are the pre requisites ?
i. to modify datatype of a column ?
ii. to add a column with NOT NULL constraint ?

To Modify the datatype of a column the column must be empty.
To add a column with NOT NULL constrain, the table must be empty.

Where the integrity constrints are stored in Data Dictionary ?

The integrity constraints are stored in USER_CONSTRAINTS.

How will you a activate/deactivate integrity constraints ?

The integrity constraints can be enabled or disabled by ALTER TABLE ENABLE constraint/DISABLE constraint.

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 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 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 a database trigger ? Name some usages of database trigger ?

Database trigger is stored PL/SQL program unit associated with a specific database table.
Usages are Audit data modificateions, Log events transparently, Enforce complex business
rules Derive column values automatically, Implement complex security authorizations.
Maintain replicate tables.

How many types of database triggers can be specified on a table ? What are they ?

Insert Update Delete

Before Row Yes Yes Yes
After Row Yes Yes Yes
Before Statement Yes Yes Yes
After Statement Yes Yes Yes

If FOR EACH ROW clause is specified, then the trigger for each Row affected by the

If WHEN clause is specified, the trigger fires according to the retruned boolean value.

Is it possible to use Transaction control Statements such a ROLLBACK or
COMMIT in Database Trigger ? Why ?

It is not possible. As triggers are defined for each table, if you use COMMIT of
ROLLBACK in a trigger, it affects logical transaction processing.

What are two virtual tables available during database trigger execution ?

The table columns are referred as OLD.column_name and NEW.column_name.
For triggers related to INSERT only NEW.column_name values only available.
For triggers related to UPDATE only OLD.column_name NEW.column_name values only
For triggers related to DELETE only OLD.column_name values only available.

What happens if a procedure that updates a column of table X is called in a database trigger of the same table ?

Mutation of table occurs.

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


How to generate query result in Text file through SQL Plus prompt?


SQL>spool c:\emp_output.txt
SQL>select * from emp;
SQL>spool off

A text file with the file name of emp_output.txt will be created in your C:\ drive.

Note: Don't forget to issue "spool off" statement. This "spool off" tells oracle to stop spooling. If you forget, all the statements will be recorded into this file until you close SQL Plus.

SQL*Plus and SQL - Part 1

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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 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.)

Do View contain Data ?

Views do not contain or store data.

Can a View based on another View ?


What are the advantages of Views ?

i. Provide an additional level of table security, by restricting access to a predetermined set of rows and columns of a table.
ii. Hide data complexity.
iii. Simplify commands for the user.
iv. Present the data in a different perpecetive from that of the base table.
v. Store complex queries.

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.

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.

What is a Sequence ?

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

How to see current user name
Sql> show user;

Change SQL prompt name

SQL> set sqlprompt ?Manimara > ?
Manimara >
Manimara >

Switch to DOS prompt
SQL> host

How do I eliminate the duplicate rows ?

SQL> delete from table_name where rowid not in (select max(rowid) from table group by duplicate_values_field_name);
SQL> delete duplicate_values_field_name dv from table_name ta where rowid <(select min(rowid) from table_name tb where ta.dv=tb.dv);
Table Emp
Empno Ename
101 Scott
102 Jiyo
103 Millor
104 Jiyo
105 Smith
delete ename from emp a where rowid < ( select min(rowid) from emp b where a.ename = b.ename);
The output like,
Empno Ename
101 Scott
102 Millor
103 Jiyo
104 Smith

How do I display row number with records?
To achive this use rownum pseudocolumn with query, like SQL> SQL> select rownum, ename from emp;
1 Scott
2 Millor
3 Jiyo
4 Smith

Display the records between two range
select rownum, empno, ename from emp where rowid in
(select rowid from emp where rownum <=&upto
select rowid from emp where rownum<&Start);
Enter value for upto: 10
Enter value for Start: 7
--------- --------- ----------
1 7782 CLARK
2 7788 SCOTT
3 7839 KING
4 7844 TURNER

I know the nvl function only allows the same data type(ie. number or char or date Nvl(comm, 0)), if commission is null then the text ?Not Applicable? want to display, instead of blank space. How do I write the query?
SQL> select nvl(to_char(comm.),'NA') from emp;
Output :

Oracle cursor : Implicit & Explicit cursors
Oracle uses work areas called private SQL areas to create SQL statements.
PL/SQL construct to identify each and every work are used, is called as Cursor.
For SQL queries returning a single row, PL/SQL declares all implicit cursors.
For queries that returning more than one row, the cursor needs to be explicitly declared.

Explicit Cursor attributes
There are four cursor attributes used in Oracle
cursor_name%Found, cursor_name%NOTFOUND, cursor_name%ROWCOUNT, cursor_name%ISOPEN

Implicit Cursor attributes
Same as explicit cursor but prefixed by the word SQL
Tips : 1. Here SQL%ISOPEN is false, because oracle automatically closed the implicit cursor after executing SQL statements.
: 2. All are Boolean attributes.

Find out nth highest salary from emp table
Enter value for n: 2

To view installed Oracle version information
SQL> select banner from v$version;