Moving a Table from one table space to another

ALTER TABLE Table_Name MOVE TABLESPACE Tablespace_Name;

Inline views are nothing but sub queries used as tables. There is no difference in performance in using views that are edxplicitly created and inline views.

Example is given below:

SQL> create view v_emp as select EMPNO , ENAME , JOB , DEPTNO from scott.emp
2 ;

View created.

SQL> set autotrace on
SQL> select EMPNO , ENAME , JOB ,scott.dept.DEPTNO ,DNAME from v_emp ,scott.dept
2 where v_emp.deptno = scott.dept.deptno
3 ;

EMPNO ENAME JOB DEPTNO DNAME
---------- ---------- --------- ---------- --------------
7782 CLARK MANAGER 10 ACCOUNTING
7839 KING PRESIDENT 10 ACCOUNTING
7934 MILLER CLERK 10 ACCOUNTING
7369 SMITH CLERK 20 RESEARCH
7876 ADAMS CLERK 20 RESEARCH
7902 FORD ANALYST 20 RESEARCH
7788 SCOTT ANALYST 20 RESEARCH
7566 JONES MANAGER 20 RESEARCH
7499 ALLEN SALESMAN 30 SALES
7698 BLAKE MANAGER 30 SALES
7654 MARTIN SALESMAN 30 SALES

EMPNO ENAME JOB DEPTNO DNAME
---------- ---------- --------- ---------- --------------
7900 JAMES CLERK 30 SALES
7844 TURNER SALESMAN 30 SALES
7521 WARD SALESMAN 30 SALES

14 rows selected.


Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=ALL_ROWS (Cost=6 Card=14 Bytes=47
6)

1 0 MERGE JOIN (Cost=6 Card=14 Bytes=476)
2 1 TABLE ACCESS (BY INDEX ROWID) OF 'DEPT' (TABLE) (Cost=2
Card=4 Bytes=52)

3 2 INDEX (FULL SCAN) OF 'PK_DEPT' (INDEX (UNIQUE)) (Cost=
1 Card=4)

4 1 SORT (JOIN) (Cost=4 Card=14 Bytes=294)
5 4 TABLE ACCESS (FULL) OF 'EMP' (TABLE) (Cost=3 Card=14 B
ytes=294)





Statistics
----------------------------------------------------------
8 recursive calls
0 db block gets
13 consistent gets
0 physical reads
0 redo size
986 bytes sent via SQL*Net to client
508 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
14 rows processed

SQL> select EMPNO , ENAME , JOB ,scott.dept.DEPTNO ,DNAME from (select EMPNO , ENAME , JOB ,deptno FROM scott.emp) iv_emp ,scott.dept
2 where iv_emp.deptno = scott.dept.deptno;

EMPNO ENAME JOB DEPTNO DNAME
---------- ---------- --------- ---------- --------------
7782 CLARK MANAGER 10 ACCOUNTING
7839 KING PRESIDENT 10 ACCOUNTING
7934 MILLER CLERK 10 ACCOUNTING
7369 SMITH CLERK 20 RESEARCH
7876 ADAMS CLERK 20 RESEARCH
7902 FORD ANALYST 20 RESEARCH
7788 SCOTT ANALYST 20 RESEARCH
7566 JONES MANAGER 20 RESEARCH
7499 ALLEN SALESMAN 30 SALES
7698 BLAKE MANAGER 30 SALES
7654 MARTIN SALESMAN 30 SALES

EMPNO ENAME JOB DEPTNO DNAME
---------- ---------- --------- ---------- --------------
7900 JAMES CLERK 30 SALES
7844 TURNER SALESMAN 30 SALES
7521 WARD SALESMAN 30 SALES

14 rows selected.


Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=ALL_ROWS (Cost=6 Card=14 Bytes=47
6)

1 0 MERGE JOIN (Cost=6 Card=14 Bytes=476)
2 1 TABLE ACCESS (BY INDEX ROWID) OF 'DEPT' (TABLE) (Cost=2
Card=4 Bytes=52)

3 2 INDEX (FULL SCAN) OF 'PK_DEPT' (INDEX (UNIQUE)) (Cost=
1 Card=4)

4 1 SORT (JOIN) (Cost=4 Card=14 Bytes=294)
5 4 TABLE ACCESS (FULL) OF 'EMP' (TABLE) (Cost=3 Card=14 B
ytes=294)





Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
11 consistent gets
0 physical reads
0 redo size
986 bytes sent via SQL*Net to client
508 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
14 rows processed

SQL> set autotrace off
SQL> spool off


Except for the recursive calls we find that there is no much difference between the two execution plans.

Oracle Interview Question

1. To see current user name
Sql> show user;

2. Change SQL prompt name
SQL> set sqlprompt “Manimara > “
Manimara >
Manimara >

3. Switch to DOS prompt
SQL> host

4. 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);
or
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); Example. 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

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

6. 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); Enter value for upto: 10 Enter value for Start: 7

ROWNUM EMPNO ENAME
--------- --------- ----------
1 7782 CLARK
2 7788 SCOTT
3 7839 KING
4 7844 TURNER

7. 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 :

NVL(TO_CHAR(COMM),'NA')
-----------------------
NA
300
500
NA
1400
NA
NA

8. 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.

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

10. Implicit Cursor attributes
Same as explicit cursor but prefixed by the word SQL

SQL%Found, SQL%NOTFOUND, SQL%ROWCOUNT, SQL%ISOPEN

Tips : 1. Here SQL%ISOPEN is false, because oracle automatically closed the implicit cursor after executing SQL statements.
: 2. All are Boolean attributes.

11. 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);

Enter value for n: 2
SAL
---------
3700

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

13. 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.

14. Display Odd/ Even number of records
Odd number of records:
select * from emp where (rowid,1) in (select rowid, mod(rownum,2) from emp);
1
3
5
Even number of records:
select * from emp where (rowid,0) in (select rowid, mod(rownum,2) from emp)
2
4
6

15. Which date function returns number value?
months_between

16. Any three PL/SQL Exceptions?
Too_many_rows, No_Data_Found, Value_Error, Zero_Error, Others

17. What are PL/SQL Cursor Exceptions?
Cursor_Already_Open, Invalid_Cursor

18. Other way to replace query result null value with a text
SQL> Set NULL ‘N/A’
to reset SQL> Set NULL ‘’

19. What are the more common pseudo-columns?
SYSDATE, USER , UID, CURVAL, NEXTVAL, ROWID, ROWNUM

20. What is the output of SIGN function?
1 for positive value,
0 for Zero,
-1 for Negative value.

21. What is the maximum number of triggers, can apply to a single table?
12 triggers.

(The maximum number of triggers that can be applied to a table is unlimited but the number of types of triggers that we can apply on table may be 12)

PL/SQL For Loops

Even when we use reverse option in for loop the intial counter should always be less than the last counter.

For example the following code will never execute

for x in reverse 12..1
loop
dbms_output.put_line('You can never read me');
end loop;


We can manipulate the range in the loops but they do not effect the execution of the loop in any way because the range scheema is executed only the time the loop begins. Any changes made to the range variables will not effect the range ounter. Its considered bad programming practice though.

FOR a_counter IN lo_val .. hi_val

LOOP

  IF a_counter > lo_val * 2

  THEN

     hi_val := lo_val;

  END IF;

END LOOP;

END LOOP;

Oracle Wrap and Excluding an Index

Wrap:
To convert PL/SQL code into binary format we can use the wrap option. wrap is availbale in oracle/ora92/bin directory
wrap will produce a file which is a binary version of the input file. The binary file can be compiled by oracle. But there is no decode option available using which you can convert back the original file from the binary version of the code. Hence it always better to store the original file as well.

How to exclude an Index:
The following are the ways in which we can make the query not to include the index on the column

1.Adding an expression to the indexed column
Eg : Select count(*) from employees where (emp_id)+0 = 1000;
2.Specifying the FULL hint to force full table scan
Eg : Select /*+ FULL(employees)*/ * from employees where emp_id = 1000;
3.Specifying NO_INDEX hint
Eg : Select /*+ NO_INDEX*/ * from employees where emp_id = 1000;
4.Using a function over the indexed column
Eg : Select * from employees where to_number(emp_id) = 1000;

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Hello World

This is my first blog entry. Will try to post regulary as i play with java and oracle.