ORACLE FREQUENTLY ASKED QUESTIONS - VI
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.
PL/SQL is a procedural language that has both interactive SQL and procedural programming language constructs such as iteration, conditional branching.
What are the components
of OEM? (For DBA)
Oracle Enterprise Manager (OEM) has the following components:
. Management Server (OMS): Middle tier server that handles communication with the intelligent agents. The OEM Console connects to the management server to monitor and configure the Oracle enterprise.
. Console: This is a graphical interface from where one can schedule jobs, events, and monitor the database. The console can be opened from a Windows workstation, Unix XTerm (oemapp command) or Web browser session (oem_webstage).
. Intelligent Agent (OIA): The OIA runs on the target database and takes care of the execution of jobs and events scheduled through the Console.
Oracle Enterprise Manager (OEM) has the following components:
. Management Server (OMS): Middle tier server that handles communication with the intelligent agents. The OEM Console connects to the management server to monitor and configure the Oracle enterprise.
. Console: This is a graphical interface from where one can schedule jobs, events, and monitor the database. The console can be opened from a Windows workstation, Unix XTerm (oemapp command) or Web browser session (oem_webstage).
. Intelligent Agent (OIA): The OIA runs on the target database and takes care of the execution of jobs and events scheduled through the Console.
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.
Mutation of table occurs.
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.
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.
How many types of
database triggers can be specified on a table? What are they?
Insert Update Delete
Before Row o.k. o.k. o.k.
After Row o.k. o.k. o.k.
Before Statement o.k. o.k. o.k.
After Statement o.k. o.k. o.k.
If FOR EACH ROW clause is specified, then the trigger for each Row affected by the statement.
If WHEN clause is specified, the trigger fires according to the returned Boolean value.
Insert Update Delete
Before Row o.k. o.k. o.k.
After Row o.k. o.k. o.k.
Before Statement o.k. o.k. o.k.
After Statement o.k. o.k. o.k.
If FOR EACH ROW clause is specified, then the trigger for each Row affected by the statement.
If WHEN clause is specified, the trigger fires according to the returned Boolean value.
What are the modes of
parameters that can be passed to a procedure?
IN,OUT,IN-OUT parameters.
IN,OUT,IN-OUT parameters.
Where the
Pre_defined_exceptions are stored?
In the standard package.
Procedures, Functions & Packages ;
In the standard package.
Procedures, Functions & Packages ;
Write the order of
precedence for validation of a column in a table?
I. done using Database triggers.
ii. done using Integarity Constraints.?
I & ii.
I. done using Database triggers.
ii. done using Integarity Constraints.?
I & ii.
Give the structure of the
function?
FUNCTION name (argument list .....) Return datatype is
local variable declarations
Begin
executable statements
Exception
execution handlers
End;
FUNCTION name (argument list .....) Return datatype is
local variable declarations
Begin
executable statements
Exception
execution handlers
End;
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');
Function is called as part of an expression.
sal := calculate_sal ('a822');
procedure is called as a PL/SQL statement
calculate_bonus ('A822');
What are advantages fo
Stored Procedures?
Extensibility,Modularity, Reusability, Maintainability and one time compilation.
Extensibility,Modularity, Reusability, Maintainability and one time compilation.
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 exceptions are.
CURSOR_ALREADY_OPEN
DUP_VAL_ON_INDEX
NO_DATA_FOUND
TOO_MANY_ROWS
INVALID_CURSOR
INVALID_NUMBER
LOGON_DENIED
NOT_LOGGED_ON
PROGRAM-ERROR
STORAGE_ERROR
TIMEOUT_ON_RESOURCE
VALUE_ERROR
ZERO_DIVIDE
OTHERS.
Exception is the error handling part of PL/SQL block. The types are Predefined and user defined. Some of Predefined exceptions are.
CURSOR_ALREADY_OPEN
DUP_VAL_ON_INDEX
NO_DATA_FOUND
TOO_MANY_ROWS
INVALID_CURSOR
INVALID_NUMBER
LOGON_DENIED
NOT_LOGGED_ON
PROGRAM-ERROR
STORAGE_ERROR
TIMEOUT_ON_RESOURCE
VALUE_ERROR
ZERO_DIVIDE
OTHERS.
What are the PL/SQL
Statements used in cursor processing?
DECLARE CURSOR name, OPEN cursor name, FETCH cursor name INTO or Record types, CLOSE cursor name.
DECLARE CURSOR name, OPEN cursor name, FETCH cursor name INTO or Record types, CLOSE cursor name.
What are the components
of a PL/SQL Block?
Declarative part, Executable part and Exception part.
Datatypes PL/SQL
Declarative part, Executable part and Exception part.
Datatypes PL/SQL
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 modifications, Log events transparently, Enforce complex business rules Derive column values automatically, Implement complex security authorizations. Maintain replicate tables.
Database trigger is stored PL/SQL program unit associated with a specific database table. Usages are Audit data modifications, Log events transparently, Enforce complex business rules Derive column values automatically, Implement complex security authorizations. Maintain replicate tables.
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.
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.
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.
e.g.. FOR emp_rec IN C1 LOOP
salary_total := salary_total +emp_rec sal;
END 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.
e.g.. FOR emp_rec IN C1 LOOP
salary_total := salary_total +emp_rec sal;
END LOOP;
What will happen after
commit statement?
Cursor C1 is
Select empno,
ename from emp;
Begin
open C1; loop
Fetch C1 into
eno.ename;
Exit When
C1 %notfound;-----
commit;
end loop;
end;
The cursor having query as SELECT .... FOR UPDATE gets closed after COMMIT/ROLLBACK.
The cursor having query as SELECT.... does not get closed even after COMMIT/ROLLBACK.
Cursor C1 is
Select empno,
ename from emp;
Begin
open C1; loop
Fetch C1 into
eno.ename;
Exit When
C1 %notfound;-----
commit;
end loop;
end;
The cursor having query as SELECT .... FOR UPDATE gets closed after COMMIT/ROLLBACK.
The cursor having query as SELECT.... does not get closed even after COMMIT/ROLLBACK.
How packaged procedures
and functions are called from the following?
a. Stored procedure or anonymous block
b. an application program such a PRC *C, PRO* COBOL
c. SQL *PLUS??
a. PACKAGE NAME.PROCEDURE NAME (parameters);
variable := PACKAGE NAME.FUNCTION NAME (arguments);
EXEC SQL EXECUTE
b.BEGIN
PACKAGE NAME.PROCEDURE NAME (parameters)
variable := PACKAGE NAME.FUNCTION NAME (arguments);
END;
END EXEC;
c. EXECUTE PACKAGE NAME.PROCEDURE if the procedures does not have any out/in-out parameters. A function cannot be called.
a. Stored procedure or anonymous block
b. an application program such a PRC *C, PRO* COBOL
c. SQL *PLUS??
a. PACKAGE NAME.PROCEDURE NAME (parameters);
variable := PACKAGE NAME.FUNCTION NAME (arguments);
EXEC SQL EXECUTE
b.BEGIN
PACKAGE NAME.PROCEDURE NAME (parameters)
variable := PACKAGE NAME.FUNCTION NAME (arguments);
END;
END EXEC;
c. EXECUTE PACKAGE NAME.PROCEDURE if the procedures does not have any out/in-out parameters. A function cannot be called.
What is a stored
procedure?
A stored procedure is a sequence of statements that perform specific function.
A stored procedure is a sequence of statements that perform specific function.
What are the components
of a PL/SQL block?
A set of related declarations and procedural statements is called block.
A set of related declarations and procedural statements is called block.
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.
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 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 cannot be accessed by other procedures.
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 cannot be accessed by other procedures.
What are the cursor
attributes used in PL/SQL?
%ISOPEN - to check whether cursor is open or not
% ROWCOUNT - number of rows fetched/updated/deleted.
% FOUND - to check whether cursor has fetched any row. True if rows are fetched.
% NOT FOUND - to check whether cursor has fetched any row. True if no rows are fetched.
These attributes are proceeded with SQL for Implicit Cursors and with Cursor name for Explicit Cursors.
%ISOPEN - to check whether cursor is open or not
% ROWCOUNT - number of rows fetched/updated/deleted.
% FOUND - to check whether cursor has fetched any row. True if rows are fetched.
% NOT FOUND - to check whether cursor has fetched any row. True if no rows are fetched.
These attributes are proceeded with SQL for Implicit Cursors and with Cursor name for Explicit Cursors.
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 are:
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.
% 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 are:
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.
% 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 are the different
types of PL/SQL program units that can be defined and stored in ORACLE database?
Procedures and Functions,Packages and Database Triggers.
Procedures and Functions,Packages and Database Triggers.
What are the advantages
of having a Package?
Increased functionality (for example,global package variables can be declared and used by any proecdure in the package) and performance (for example all objects of the package are parsed compiled, and loaded into memory once)
Increased functionality (for example,global package variables can be declared and used by any proecdure in the package) and performance (for example all objects of the package are parsed compiled, and loaded into memory once)
What are the uses of
Database Trigger?
Database triggers can be used to automatic data generation, audit data modifications, enforce complex Integrity constraints, and customize complex security authorizations.
Database triggers can be used to automatic data generation, audit data modifications, enforce complex Integrity constraints, and customize complex security authorizations.
What is a Procedure?
A Procedure consist of a set of SQL and PL/SQL statements that are grouped together as a unit to solve a specific problem or perform a set of related tasks.
A Procedure consist of a set of SQL and PL/SQL statements that are grouped together as a unit to solve a specific problem or perform a set of related tasks.
What is a Package?
A Package is a collection of related procedures, functions, variables and other package constructs together as a unit in the database.
A Package is a collection of related procedures, functions, variables and other package constructs together as a unit in the database.
What is difference
between Procedures and Functions?
A Function returns a value to the caller where as a Procedure does not.
A Function returns a value to the caller where as a Procedure does not.
What is Database Trigger?
A Database Trigger is procedure (set of SQL and PL/SQL statements) that is automatically executed as a result of an insert in, update to, or delete from a table.
A Database Trigger is procedure (set of SQL and PL/SQL statements) that is automatically executed as a result of an insert in, update to, or delete from a table.
Can the default values be
assigned to actual parameters?
Yes
Yes
Can a primary key contain
more than one columns?
Yes
Yes
What is an UTL_FILE.What
are different procedures and functions associated with it?
UTL_FILE is a package that adds the ability to read and write to operating system files. Procedures associated with it are FCLOSE, FCLOSE_ALL and 5 procedures to output data to a file PUT, PUT_LINE, NEW_LINE, PUTF, FFLUSH.PUT, FFLUSH.PUT_LINE,FFLUSH.NEW_LINE. Functions associated with it are FOPEN, ISOPEN.
UTL_FILE is a package that adds the ability to read and write to operating system files. Procedures associated with it are FCLOSE, FCLOSE_ALL and 5 procedures to output data to a file PUT, PUT_LINE, NEW_LINE, PUTF, FFLUSH.PUT, FFLUSH.PUT_LINE,FFLUSH.NEW_LINE. Functions associated with it are FOPEN, ISOPEN.
What are ORACLE
PRECOMPILERS?
Using ORACLE PRECOMPILERS, SQL statements and PL/SQL blocks can be contained inside 3GL programs written in C,C++,COBOL,PASCAL, FORTRAN,PL/1 AND ADA. The Precompilers are known as Pro*C,Pro*Cobol,... This form of PL/SQL is known as embedded pl/sql,the language in which pl/sql is embedded is known as the host language. The prcompiler translates the embedded SQL and pl/sql statements into calls to the precompiler runtime library. The output must be compiled and linked with this library to creator an executable.
Using ORACLE PRECOMPILERS, SQL statements and PL/SQL blocks can be contained inside 3GL programs written in C,C++,COBOL,PASCAL, FORTRAN,PL/1 AND ADA. The Precompilers are known as Pro*C,Pro*Cobol,... This form of PL/SQL is known as embedded pl/sql,the language in which pl/sql is embedded is known as the host language. The prcompiler translates the embedded SQL and pl/sql statements into calls to the precompiler runtime library. The output must be compiled and linked with this library to creator an executable.
Differentiate between
TRUNCATE and DELETE?
TRUNCATE deletes much faster than DELETE
TRUNCATE
DELETE
It is a DDL statement
It is a DML statement
It is a one way trip, cannot ROLLBACK
One can Rollback
Doesn't have selective features (where clause)
Has
Doesn't fire database triggers
Does
It requires disabling of referential constraints.
TRUNCATE deletes much faster than DELETE
TRUNCATE
DELETE
It is a DDL statement
It is a DML statement
It is a one way trip, cannot ROLLBACK
One can Rollback
Doesn't have selective features (where clause)
Has
Doesn't fire database triggers
Does
It requires disabling of referential constraints.
What is difference
between a formal and an actual parameter?
The variables declared in the procedure and which are passed, as arguments are called actual, the parameters in the procedure declaration. Actual parameters contain the values that are passed to a procedure and receive results. Formal parameters are the placeholders for the values of actual parameters
The variables declared in the procedure and which are passed, as arguments are called actual, the parameters in the procedure declaration. Actual parameters contain the values that are passed to a procedure and receive results. Formal parameters are the placeholders for the values of actual parameters
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
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
-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 '-')
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.
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 whereas SQL and PL/SQL language interface and reporting tool. It’s 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.
SQL*PLUS is a command line tool whereas SQL and PL/SQL language interface and reporting tool. It’s 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: It’s a join foreign key of a table references the same table.
Self-join: It’s a join foreign key of a table references the same table.
Outer Join: It’s 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: It’s 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.
Equi-join: It’s 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.
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
-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);
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 < sal
-- group by level
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 < sal
-- group by level
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.
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?
PL/SQL declares a cursor implicitly for all SQL data manipulation statements, including queries that return only one row. However, queries that return more than one row you must declare an explicit cursor or use a cursor FOR loop.
PL/SQL declares a cursor implicitly for all SQL data manipulation statements, including queries that return 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 an OUTER JOIN?
Outer Join: It’s 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.
Outer Join: It’s 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.
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.
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
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.
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
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
-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.
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 query does 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.
NO DATA FOUND is an exception raised only for the SELECT....INTO statements when the where clause of the query does 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
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;
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
INSTR('120000 12 0 .125',1,'.')
output 13
What are different modes
of parameters used in functions and procedures?
-IN -OUT –INOUT
-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.
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.
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.
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.
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
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);
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.
-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.
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
By using DISTINCT
What is a view?
A view is stored procedure based on one or more tables, it’s a virtual table.
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.
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.
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.
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
1,000,00
What are cursor
attributes?
-%ROWCOUNT
-%NOTFOUND
-%FOUND
-%ISOPEN
-%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 '%'.
'' 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.
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
Using ROWID.CONSTRAINTS
What is difference
between TRUNCATE & DELETE?
TRUNCATE commits after deleting entire table i.e., cannot 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.
TRUNCATE commits after deleting entire table i.e., cannot 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.
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 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.
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.
The integrity constraints are stored in USER_CONSTRAINTS.
What is the Sub-query?
Sub query is a query whose return values are used in filtering conditions of the main query.
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.
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.
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.
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.
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.
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.
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.
If a 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.
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.
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.
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.
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:
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. Let’s 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.
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.
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.
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.
Correlated sub query is a sub query which has reference to the main query.
What are the data types
allowed in a table?
CHAR
CHAR
VARCHAR2
NUMBER
DATE
RAW
LONG
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.
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.
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 Co-ordinations 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)
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
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
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
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
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)
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
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..
Either rman or alter tablespace begin backup will do..
How many types of Sql
Statements are there in Oracle
There are basically 6 types of sql statements. 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 .ex: Alter Statements, Set Role
e) System Control Statements: Change Properties of Oracle Instance .ex. Alter System
f) Embedded Sql: Incorporate DDL, DML and T.C.S in Programming Language. ex: Using the Sql Statements in languages such as 'C', Open, Fetch, execute and close
There are basically 6 types of sql statements. 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 .ex: Alter Statements, Set Role
e) System Control Statements: Change Properties of Oracle Instance .ex. Alter System
f) Embedded Sql: Incorporate DDL, DML and T.C.S in Programming Language. ex: 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.
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.
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.
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)
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
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
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 an 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) Archives(ARCH) :- The Archiver copies online redo log files to archival storage 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.
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 an 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) Archives(ARCH) :- The Archiver copies online redo log files to archival storage 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.
: - 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.
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.
What are Procedure,
functions and Packages?
·
Procedures
and functions consist of set of PL/SQL statements that are grouped together as
a unit to solve a specific problem or perform set of related tasks.
·
Procedures
do not return values while Functions return one value
·
Packages
provide a method of encapsulating and storing related procedures, functions,
variables and other Package Contents
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