The SET options FEEDBACK and VERIFY can be set to OFF.

77.       How do you generate file output from SQL

By use of the SPOOL comm

78.       What is a CO-RELATED SUBQUERY

A CO-RELATED SUBQUERY is one that has a correlation name as table or view designator in the FROM clause of the outer query and the same correlation name as a qualifier of a search condition in the WHERE clause of the subquery.

eg
     SELECT  field1 from table1 X
     WHERE  field2>(select avg(field2) from table1 Y
                                       where
                                       field1=X.field1);


(The subquery in a correlated subquery is revaluated for every row of the table or view named in the outer query.)

 

79. What are various joins used while writing SUBQUERIES


Self join-Its a join foreign key of a table references the same table.

Outer Join–Its a join condition used where One can query all the rows of one of the tables in the join condition even though they don’t satisfy the join condition.

Equi-join–Its a join condition that retrieves rows from one or more tables in which one or more columns in one table are equal to one or more columns in the second table.

 

80.What are various constraints used in SQL

NULL
NOT NULL
CHECK
DEFAULT

 

81.What are different Oracle database objects

TABLES
VIEWS
INDEXES
SYNONYMS
SEQUENCES
TABLESPACES etc

 

82. 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.

 

83. What is a view


A view is stored procedure based on one or more tables, its a virtual table.

 

84. What are various privileges that a user can grant to another user


SELECT
CONNECT
RESOURCE

 

85. 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.

 

86. Can a primary key contain more than one columns


Yes

 

87. How you will avoid duplicating records in a query


By using DISTINCT

 

88. What is difference between SQL and SQL*PLUS

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

 

89. Which datatype is used for storing graphics and images


LONG RAW data type is used for storing BLOB’s (binary large objects).

 

90. How will you delete duplicating rows from a base table


DELETE FROM table_name A WHERE rowid>(SELECT min(rowid) from table_name B where B.table_no=A.table_no);

CREATE TABLE new_table AS SELECT DISTINCT * FROM old_table;

DROP old_table RENAME new_table TO old_table DELETE FROM table_name A WHERE rowid NOT IN (SELECT MAX(ROWID) FROM table_name GROUP BY column_name)

 

91. 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 ‘-‘)

 

92. 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

 

93. There is a ‘%’ sign in one field of a column. What will be the query to find it.


‘\’ Should be used before ‘%’.

 

94. When you use WHERE clause and when 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.

 

95. Which is more faster – IN or EXISTS


EXISTS is more faster than IN because EXISTS returns a Boolean value whereas IN returns a value.

 

96. What is a OUTER JOIN


Outer Join–Its a join condition used where you can query all the rows of one of the tables in the join condition even though they dont satisfy the join condition.

 

97. 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



98. What is a pseudo column. Give some examples


It is a column that is not an actual column in the table.

eg USER, UID, SYSDATE, ROWNUM, ROWID, NULL, AND LEVEL.

Suppose customer table is there 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)

 

99. 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.

 

100.           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.

 

101.           Difference between an implicit & an explicit cursor.


PL/SQL declares a cursor implicitly for all SQL data manipulation statements, including quries 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.

 

102            What are cursor attributes


%ROWCOUNT
%NOTFOUND
%FOUND
%ISOPEN

 

103 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.

 

 

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