ANSWER:

Result of the subquery is small Then “IN” is typicaly more appropriate.
and
Result of the subquery is big/large/long Then “EXIST” is more appropriate.

suppose :-
[CODE]
select * from table_1
where id in (select Id from table_2)
[/CODE]

Is normaly processed as:

[CODE]
select * from table_1 , ( select distinct y from table_2 ) t2
where table_1.x = table_2.y;
[/CODE]

Means the subquery is evaluated, distinct’ed, indexed (or hashed or sorted) and then joined to the original table

and oposite is (EXIST)
[CODE]
select * from table_1 where exists ( select null from table_2 where table_2.y = table_1.x )

[/CODE]

That is processed more like:

[CODE]
for x in ( select * from table_1 ) loop
if ( exists ( select null from table_2 where table_2.y = x.x ) then
OUTPUT THE RECORD end
end if
end loop

[/CODE]

It always results in a full scan of Table_1 whereas the first query can make use of an index on Table_1(x).

For this can be Use Direct Load Insert
——————————————————-
Direct Load Insert is a faster way of running an INSERT statement.Direct Load Insert
differs from Conventional Insert in that it bypasses the buffer cache.

To use Direct Load Insert, add the APPEND hint to your INSERT statement. like below…..

INSERT /*+ APPEND*/
INTO target_table
SELECT * FROM source_table

Need to know for Direct load Insert
—————————————————
1. Data is appended to the table. Existing free space is not re-used.
2. Direct Load Insert only works for INSERT INTO .. SELECT …. Inserts
3. Direct Load Insert uses rollback segments to maintain indexes as the data is loaded
4. Direct Load Insert can be run with a NOLOGGING option making it even faster.
5. Direct Load Insert locks the table in exclusive mode. No other session can insert, update, or delete data, or maintain any indexes.
6. Referential Integrity (Foreign Key) constraints and triggers must be disabled before running Direct Path Insert
7. Direct Load Insert cannot occur on:
o Index Organised Tables
o Tables with LOB Columns
o Tables with Object Columns
o Clustered Tables

DEMO
=====
[CODE]

SQL*Plus: Release 10.2.0.1.0 – Production on Sat Jul 31 12:28:13 2010

Copyright (c) 1982, 2005, Oracle.  All rights reserved.

SQL> conn basel2@test107
Enter password:
Connected.
SQL>
SQL>
SQL>
SQL> set timing on
SQL> set time on
12:28:41 SQL>
12:28:42 SQL>
12:28:42 SQL> create table direct_load_insert as select * from TABLE_OF_VIEW_BACKUP
12:30:57   2  where brancd=0 ;

Table created.

Elapsed: 00:00:04.03
12:31:28 SQL>
12:31:31 SQL> desc  direct_load_insert
Name                                      Null?    Type
—————————————– ——– —————————-
BRANCD                                             VARCHAR2(3)
ACTYPE                                             VARCHAR2(3)
ACTNUM                                             VARCHAR2(12)
CURBAL                                             NUMBER
LONCON                                             VARCHAR2(3)
ACTTIT                                             VARCHAR2(60)
CUSCOD                                             VARCHAR2(10)
SHDESC                                             VARCHAR2(10)
OPNDAT                                             DATE
EXPDAT                                             DATE
SECURITY_BAL                                       NUMBER
SECURITY_TYPE                                      VARCHAR2(4000)
VALDAT                                             DATE
CATGRY                                             VARCHAR2(1)
VALPRD                                             NUMBER(4)
LCAAMT                                             NUMBER(16,3)
REMAMT                                             NUMBER(16,3)
BANCOD                                             VARCHAR2(3)
CMPIND                                             VARCHAR2(1)
REMARK                                             VARCHAR2(50)

12:31:48 SQL>
12:31:50 SQL>
12:31:51 SQL> INSERT /*+ APPEND*/
12:32:19   2  INTO direct_load_insert
12:32:44   3  SELECT * FROM TABLE_OF_VIEW_BACKUP ;

3706656 rows created.

Elapsed: 00:01:13.31
12:34:17 SQL>
12:34:23 SQL>
12:34:23 SQL>
12:34:23 SQL> ROLLBACK ;

Rollback complete.

Elapsed: 00:00:00.06
12:34:53 SQL>
12:34:54 SQL>
12:34:54 SQL> INSERT INTO direct_load_insert
12:35:31   2  SELECT * FROM TABLE_OF_VIEW_BACKUP ;

3706656 rows created.

Elapsed: 00:01:53.36
12:37:30 SQL>
12:38:06 SQL>
12:38:06 SQL> ROLLBACK
12:39:44   2  /

Rollback complete.

Elapsed: 00:01:25.35
12:41:12 SQL>
12:41:14 SQL>
12:41:14 SQL> DROP TABLE direct_load_insert ;

Table dropped.

Elapsed: 00:00:28.17
12:41:57 SQL>
12:41:59 SQL>
12:41:59 SQL>

[/CODE]

Script for practice ..

drop table emp_halim;

CREATE TABLE emp_halim  AS SELECT * FROM emp;

SET DEFINE OFF;
Insert into EMP_HALIM
 (EMPNO, ENAME, JOB, MGR, HIREDATE,
 SAL, COMM, DEPTNO)
 Values
 (7999, 'halim', 'CLERK', 7782, TO_DATE('01/23/1982 00:00:00', 'MM/DD/YYYY HH24:MI:SS'),
 1300, NULL, 70);
Insert into EMP_HALIM
 (EMPNO, ENAME, JOB, MGR, HIREDATE,
 SAL, COMM, DEPTNO)
 Values
 (7989, 'halim', 'CLERK', 7782, TO_DATE('01/23/1982 00:00:00', 'MM/DD/YYYY HH24:MI:SS'),
 1300, NULL, 60);
Insert into EMP_HALIM
 (EMPNO, ENAME, JOB, MGR, HIREDATE,
 SAL, COMM, DEPTNO)
 Values
 (7979, 'halim', 'CLERK', 7782, TO_DATE('01/23/1982 00:00:00', 'MM/DD/YYYY HH24:MI:SS'),
 1300, NULL, 50);
COMMIT;

SELECT *
 FROM emp_halim;

----------------------------------------------

drop table dept_halim;

CREATE TABLE dept_halim AS SELECT * FROM dept;

SELECT *
 FROM dept_halim;

UPDATE emp_halim a
 SET ename = (SELECT dname
 FROM dept_halim b
 WHERE a.deptno = b.deptno)

 rollback ;

UPDATE emp_halim a
 SET ename = (SELECT dname
 FROM dept_halim b
 WHERE a.deptno = b.deptno)
 WHERE EXISTS (SELECT dname
 FROM dept_halim b
 WHERE a.deptno = b.deptno);

rollback;

Example :——————-

SQL*Plus: Release 10.2.0.1.0 - Production on Mon Jul 12 18:27:34 2010

Copyright (c) 1982, 2005, Oracle.  All rights reserved.

SQL> conn scott@test107
Enter password:
Connected.
SQL>
SQL>
SQL> set linesize 1000
SQL> set pagesize 1000
SQL>
SQL> UPDATE emp_halim a
 2     SET ename = (SELECT dname
 3                    FROM dept_halim b
 4  /
 FROM dept_halim b
 *
ERROR at line 3:
ORA-00907: missing right parenthesis

SQL>
SQL> drop table emp_halim;

Table dropped.

SQL>
SQL>
SQL> CREATE TABLE emp_halim  AS SELECT * FROM emp;

Table created.

SQL>
SQL>
SQL> SET DEFINE OFF;
SQL> Insert into EMP_HALIM
 2     (EMPNO, ENAME, JOB, MGR, HIREDATE,
 3      SAL, COMM, DEPTNO)
 4   Values
 5     (7999, 'halim', 'CLERK', 7782, TO_DATE('01/23/1982 00:00:00', 'MM/DD/YYYY HH24:MI:SS'),
 6      1300, NULL, 70);

1 row created.

SQL> Insert into EMP_HALIM
 2     (EMPNO, ENAME, JOB, MGR, HIREDATE,
 3      SAL, COMM, DEPTNO)
 4   Values
 5     (7989, 'halim', 'CLERK', 7782, TO_DATE('01/23/1982 00:00:00', 'MM/DD/YYYY HH24:MI:SS'),
 6      1300, NULL, 60);

1 row created.

SQL> Insert into EMP_HALIM
 2     (EMPNO, ENAME, JOB, MGR, HIREDATE,
 3      SAL, COMM, DEPTNO)
 4   Values
 5     (7979, 'halim', 'CLERK', 7782, TO_DATE('01/23/1982 00:00:00', 'MM/DD/YYYY HH24:MI:SS'),
 6      1300, NULL, 50);

1 row created.

SQL> COMMIT;

Commit complete.

SQL>
SQL>
SQL> SELECT *
 2    FROM emp_halim;

 EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
 7369 SMITH      CLERK           7902 17-DEC-80       1000                    20
 7521 WARD       SALESMAN        7698 22-FEB-81       1250        500         30
 7566 JONES      MANAGER         7839 02-APR-81       2975                    20
 7654 MARTIN     SALESMAN        7698 28-SEP-81       1250       1400         30
 7698 BLAKE      MANAGER         7839 01-MAY-81       2850                    30
 7782 CLARK      MANAGER         7839 09-JUN-81       2450                    10
 7788 SCOTT      ANALYST         7566 19-APR-87       3000                    20
 7839 KING       PRESIDENT            17-NOV-81       5000                    10
 7844 TURNER     SALESMAN        7698 08-SEP-81       1500          0         30
 7876 ADAMS      CLERK           7788 23-MAY-87       1100                    20
 7900 JAMES      CLERK           7698 03-DEC-81        950                    30
 7902 FORD       ANALYST         7566 03-DEC-81       3000                    20
 7934 MILLER     CLERK           7782 23-JAN-82       1300                    10
 7999 halim      CLERK           7782 23-JAN-82       1300                    70
 7989 halim      CLERK           7782 23-JAN-82       1300                    60
 7979 halim      CLERK           7782 23-JAN-82       1300                    50

16 rows selected.

SQL>
SQL>
SQL>
SQL>
SQL>
SQL>
SQL> drop table dept_halim;

Table dropped.

SQL>
SQL>
SQL> CREATE TABLE dept_halim AS SELECT * FROM dept;

Table created.

SQL>
SQL> SELECT *
 2    FROM dept_halim;

 DEPTNO DNAME          LOC
---------- -------------- -------------
 10 ACCOUNTING     NEW YORK
 20 RESEARCH       DALLAS
 30 SALES          CHICAGO
 40 OPERATIONS     BOSTON

SQL>
SQL>
SQL>
SQL> UPDATE emp_halim a
 2     SET ename = (SELECT dname
 3                    FROM dept_halim b
 4                   WHERE a.deptno = b.deptno);

16 rows updated.

SQL>
SQL> rollback ;

Rollback complete.

SQL>
SQL>
SQL>
SQL> UPDATE emp_halim a
 2     SET ename = (SELECT dname
 3                    FROM dept_halim b
 4                   WHERE a.deptno = b.deptno)
 5   WHERE EXISTS (SELECT dname
 6                   FROM dept_halim b
 7                  WHERE a.deptno = b.deptno);

13 rows updated.

SQL>
SQL>
SQL>
SQL>
SQL>

Cause:        rollback records needed by a reader for consistent read are overwritten
by other writers
Action:    If in Automatic Undo Management mode, increase undo_retention setting.
Otherwise, use larger rollback segmentsde, increase undo_retention setting.
Otherwise, use larger rollback segments

There are some situations that can cause the ORA-01555 error:

1. An active database with an insufficient number of small-sized rollback segments

2. A rollback segment corruption that prevents a consistent read requested by the query

3. A fetch across commits while your cursor is open

in last point(3) here is my concern :
Its happen when an “commit” is use in a loop or  inside a procedure frequently or or  inside a application frequently.

I am highlighted it just to understood that : try to not use “commit” inside loop
or inside procedure in your application so frequently. it is a bad logic.

What are the differences in syntax between a CASE statement
and a CASE expression ?
===========================================================

The CASE expression was first added to SQL in Oracle8i.
Oracle9i extends its support to PL/SQL to allow CASE to
be used as an expression or statement:

1. A CASE statement is terminated with END CASE, while a CASE
expression is terminated with END.

2. The code within a WHEN clause of a CASE statement must terminate
with a semi-colon; the code within a WHEN clause of a CASE expression
must not terminate with a semi-colon.

Example:=

Case expression:
==================

SELECT ename, empno,
(CASE
WHEN sal < 1000 THEN 'Low'
WHEN sal BETWEEN 1000 AND 3000 THEN 'Medium'
WHEN sal > 3000 THEN 'High'
ELSE 'N/A'
END) salary
FROM emp
ORDER BY ename;

Case statement:
==================

</pre>
SET SERVEROUTPUT ON
BEGIN
FOR cur_rec IN (SELECT ename, empno, sal FROM emp ORDER BY ename) LOOP
DBMS_OUTPUT.PUT(cur_rec.ename || ' : ' || cur_rec.empno || ' : ');
CASE
WHEN cur_rec.sal < 1000 THEN
DBMS_OUTPUT.PUT_LINE('Low');
WHEN cur_rec.sal BETWEEN 1000 AND 3000 THEN
DBMS_OUTPUT.PUT_LINE('Medium');
WHEN cur_rec.sal > 3000 THEN
DBMS_OUTPUT.PUT_LINE('High');
ELSE
DBMS_OUTPUT.PUT_LINE('Unknown');
END CASE;
END LOOP;
END;
/
<pre>

=============================================================
When I execute a export (EXP) in this version I found this result……………………….
—————————————————————————-
—————————————————————————
==============================================================

SQL*Plus: Release 11.1.0.6.0 – Production on Thu Jul 8 13:00:12 2010

Copyright (c) 1982, 2007, Oracle.  All rights reserved.

SQL> host
Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.

C:\Documents and Settings\era-1>exp userid=basel2/basel2@test107 owner=basel2
file=D:\basel_dump\basel2_08072010_test107.dmp LOG=D:\basel_dump\basel2_08072010_test107.LOG

Export: Release 11.1.0.6.0 – Production on Thu Jul 8 13:00:19 2010

Copyright (c) 1982, 2007, Oracle.  All rights reserved.

Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 – Produc
tion
With the Partitioning, Oracle Label Security, OLAP and Data Mining Scoring Engin
e options
Export done in WE8MSWIN1252 character set and AL16UTF16 NCHAR character set

About to export specified users …
. exporting pre-schema procedural objects and actions
. exporting foreign function library names for user BASEL2
. exporting PUBLIC type synonyms
. exporting private type synonyms
. exporting object type definitions for user BASEL2
About to export BASEL2′s objects …
. exporting database links
. exporting sequence numbers
. exporting cluster definitions
. about to export BASEL2′s tables via Conventional Path …
. . exporting table              AUDIT_SOURCE_HIST
EXP-00008: ORACLE error 904 encountered
ORA-00904: “MAXSIZE”: invalid identifier
. . exporting table             AUDIT_TABLE_BASEL2
EXP-00008: ORACLE error 1003 encountered
ORA-01003: no statement parsed
. . exporting table                D_TABLE_OF_VIEW
EXP-00008: ORACLE error 904 encountered
ORA-00904: “MAXSIZE”: invalid identifier
. . exporting table                 LK_BANK_RATING
EXP-00008: ORACLE error 1003 encountered
ORA-01003: no statement parsed
. . exporting table                  LK_CUS_RATING
EXP-00008: ORACLE error 904 encountered
ORA-00904: “MAXSIZE”: invalid identifier
. . exporting table              LK_GL_ELI_CAPITAL
EXP-00008: ORACLE error 1003 encountered
ORA-01003: no statement parsed
====================================================================================

Note:  As I know this is a bug of 11.1.0.6 oracle version

Look at metalink note 741984.1.
Bug number is 5872788 – there exists patch as well.

solution for another oracle versions (not sure)
================================
If there been any changes made to the database. Like catexp.sql
then you should be re-running catalog.sql which will run catexp.sql.

=====================================================================================

========================================================
But When I execute same comman here I found this result……………………….
—————————————————————————-
—————————————————————————
=========================================================

SQL*Plus: Release 10.2.0.1.0 – Production on Thu Jul 8 13:06:51 2010

Copyright (c) 1982, 2005, Oracle.  All rights reserved.

SQL> conn stlbas/stlbas@test107
Connected.
SQL>
SQL>
SQL> host
Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.

C:\Documents and Settings\era-1>
C:\Documents and Settings\era-1>exp userid=basel2/basel2@test107 owner=basel2
file=D:\basel_dump\basel2_08072010_test107.dmp LOG=D:\basel_dump\basel2_08072010_test107.LOG

Export: Release 10.2.0.1.0 – Production on Thu Jul 8 13:07:28 2010

Copyright (c) 1982, 2005, Oracle.  All rights reserved.

Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 – Production
With the Partitioning, Oracle Label Security, OLAP and Data Mining Scoring Engine options
Export done in WE8MSWIN1252 character set and AL16UTF16 NCHAR character set

About to export specified users …
. exporting pre-schema procedural objects and actions
. exporting foreign function library names for user BASEL2
. exporting PUBLIC type synonyms
. exporting private type synonyms
. exporting object type definitions for user BASEL2
About to export BASEL2′s objects …
. exporting database links
. exporting sequence numbers
. exporting cluster definitions
. about to export BASEL2′s tables via Conventional Path …
. . exporting table              AUDIT_SOURCE_HIST     138789 rows exported
. . exporting table             AUDIT_TABLE_BASEL2        457 rows exported
. . exporting table                D_TABLE_OF_VIEW          0 rows exported
. . exporting table                 LK_BANK_RATING        193 rows exported
. . exporting table                  LK_CUS_RATING         27 rows exported
. . exporting table              LK_GL_ELI_CAPITAL         18 rows exported
. . exporting table                      LK_GL_MKR         46 rows exported
. . exporting table                      LK_GL_OFF       1419 rows exported
. . exporting table                    LK_GL_OFF_1         33 rows exported
. . exporting table                       LK_GL_ON        504 rows exported
. . exporting table              LK_GL_ON_10122009      18221 rows exported
. . exporting table          LK_GL_ON_30062010_BCK        499 rows exported