Oracle-L: RE: Need help to rewrite sql statement to improve performance

From: Richard Ji <richard.ji_at_mobilespring.com>
Date: Wed, 23 Apr 2003 12:57:04 -0800
Message-ID: <F001.005880F4.20030423125704@fatcity.com>

Dick,

Not true for IS NOT NULL:

SQL> select * from t;

ID NAME
---------- ----------

         1 aaa
         2
         3 bbb

SQL> select count(*) from t where name is not null;

COUNT(*)

Elapsed: 00:00:00.01

Execution Plan

0 SELECT STATEMENT Optimizer=CHOOSE (Cost=1 Card=1 Bytes=2) 1 0 SORT (AGGREGATE)

   2    1     INDEX (FULL SCAN) OF 'T_IDX' (NON-UNIQUE) (Cost=1 Card=2
           Bytes=4)

-----Original Message-----
Sent: Wednesday, April 23, 2003 3:17 PM
To: Multiple recipients of list ORACLE-L

I'm afraid your porked. Using 'is NULL' or 'is not NULL' forces a full table scan.

Dick Goulet
Senior Oracle DBA
Oracle Certified 8i DBA

-----Original Message-----
Sent: Wednesday, April 23, 2003 12:02 PM To: Multiple recipients of list ORACLE-L

We have SQL statement use "is NOT null" and this sql statement use 2.5 million memory I/O. Does their has way to improve it? Thanks.

select count(*) FROM EMP_TABLE

where hire_date is not null
and work_date is not null
~

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