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oracle tutorial 8
Posted Date: 11 Mar 2008 Resource Type: Articles/Knowledge Sharing Category: Placement Papers
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Posted By: ramya Member Level: Gold
Rating:  Points: 5
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Super Dynamism in Cursors is obtained by passing the values as parameters( ie pass by value)
ie., for x in c1(a,b) Multiple Cursors : These are nothing but nested cursors........... In Implicit Cursors there is no need of declaration of cursors, by default system will create a cursor whenever a query is written...and the conditions are like if SQL%NOTFOUND
if SQL%ROWCOUNT > 2 will keep a count of the number of records updated.
SQL is a keyword and cannot be used to name as a cursor name explicitly.
Difference between group functions and single row functions ?
Group Function Single Row Function A group function operates A single row function on many rows returns one and result for one row. returns single result.
Not allowed in Pl/sql procedural Allowed in Pl/Sql Procedural statements
eg SUM(),AVG,MIN,MAX etc eg UPPER,LOWER,CHR...
Difference between DECODE and TRANSLATE ?
DECODE is value by value TRANSLATE is character by character replacement. replacement. Ex SELECT DECODE('ABC','A',1,'B',2,'ABC',3) eg SELECT
from dual; o/p 3 TRANSLATE('ABCGH', 'ABCDEFGHIJ', 1234567899) FROM DUAL; o/p 12378 (DECODE command is used to bring IF,THEN,ELSE logic to SQL.It tests for the IF values(s) and
then aplies THEN value(s) when true, the ELSE value(s) if not.)
Difference 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 One can Rollback ROLLBACK
Doesn't have selective features (where clause) Has Doesn't fire database triggers Does It requires disabling of referential Does not require constraints.
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.) What are various joins used while writing SUBQUERIES ? Self join-Its a join foreign key of a table references the same table.
Outer Join--Its a join condition used where One can query all the rows of one of the
tables in the join condition even though they don't satisfy the join condition.
Equi-join--Its a join condition that retrieves rows from one or more tables in which one
or more columns in one table are equal to one or more columns in the second table.
What are various constraints used in SQL ? NULL, NOT NULL, CHECK, DEFAULT
What are different Oracle database objects ? TABLES, VIEWS, INDEXES, SYNONYMS, SEQUENCES, TABLESPACES etc
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.
What is a view ? A view is stored procedure based on one or more tables, it's a virtual table.
What are various privileges that a user can grant to another user ? SELECT, CONNECT, RESOURCES
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.
Can a primary key contain more than one columns ? Yes
How you will avoid duplicating records in a query ?
By using DISTINCT
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.
Which datatype is used for storing graphics and images ? LONG RAW data type is used for storing BLOB's (binary large objects).
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)
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