Comments on: Using index for IS NULL http://www.oracloid.com/2006/05/using-index-for-is-null/ The Alex Gorbachev Oracle Blog Sun, 12 Oct 2008 19:12:01 +0000 http://wordpress.org/?v=2.5.1 By: Oracloid http://www.oracloid.com/2006/05/using-index-for-is-null/#comment-123 Oracloid Fri, 30 Jun 2006 19:05:46 +0000 http://blog.oracloid.com/?p=7#comment-123 I guess this is correct from CBO point of view. Probably, there are too few rows to use the index so optimizer estimates the cost to be lower to go for FTS. Try running these queries with autotrace and that run them with hint /*+ index(t) */. Than compare the cost of using index vs. FTS. I guess this is correct from CBO point of view.
Probably, there are too few rows to use the index so optimizer estimates the cost to be lower to go for FTS. Try running these queries with autotrace and that run them with hint /*+ index(t) */. Than compare the cost of using index vs. FTS.

]]> By: Kaleem Ullah http://www.oracloid.com/2006/05/using-index-for-is-null/#comment-120 Kaleem Ullah Fri, 30 Jun 2006 15:47:23 +0000 http://blog.oracloid.com/?p=7#comment-120 Hi, I tried this code but its not working, Please help, thanks in advance CREATE TABLE t (pcol NUMBER , ncol VARCHAR2(10) NULL , c CHAR(1) DEFAULT '1' NOT NULL ); INSERT INTO t ( pcol , ncol , c ) VALUES ( 1 , 'name1' , 1 ); INSERT INTO t ( pcol , ncol , c ) VALUES ( NULL , 'name2' , 2 ); INSERT INTO t ( pcol , ncol , c ) VALUES ( 3 , NULL , 3 ); INSERT INTO t ( pcol , ncol , c ) VALUES ( NULL , NULL , 4 ); INSERT INTO t ( pcol , ncol , c ) VALUES ( 4 , NULL , 4 ); INSERT INTO t ( pcol , ncol , c ) VALUES ( 5 , 'name3' , 2 ); CREATE INDEX t_ind ON t (ncol,c); BEGIN DBMS_STATS.gather_table_stats ( USER , 'T'); END; --This query is not usng index Select * from t where ncol = 2 --This query is not usng index Select * from t where ncol is null Hi,
I tried this code but its not working, Please help, thanks in advance

CREATE TABLE t (pcol NUMBER , ncol VARCHAR2(10) NULL , c CHAR(1) DEFAULT ‘1′ NOT NULL );

INSERT INTO t ( pcol , ncol , c ) VALUES ( 1 , ‘name1′ , 1 );
INSERT INTO t ( pcol , ncol , c ) VALUES ( NULL , ‘name2′ , 2 );
INSERT INTO t ( pcol , ncol , c ) VALUES ( 3 , NULL , 3 );
INSERT INTO t ( pcol , ncol , c ) VALUES ( NULL , NULL , 4 );
INSERT INTO t ( pcol , ncol , c ) VALUES ( 4 , NULL , 4 );
INSERT INTO t ( pcol , ncol , c ) VALUES ( 5 , ‘name3′ , 2 );

CREATE INDEX t_ind ON t (ncol,c);

BEGIN
DBMS_STATS.gather_table_stats ( USER , ‘T’);
END;

–This query is not usng index
Select * from t where ncol = 2

–This query is not usng index
Select * from t where ncol is null

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