Hi,
I have a:
- table opinion
- index CREATE INDEX opinionClassNameIndex ON OPINION(CLASSNAME )
This query is very fast and use index:
select count(*) from opinion where className like 'opinion%';
307 ms
SELECT
COUNT(*)
FROM PUBLIC.OPINION
/* PUBLIC.OPINIONCLASSNAMEINDEX: CLASSNAME >= 'opinion'
AND CLASSNAME < 'opinioo'
*/
/* scanCount: 944400 */
WHERE CLASSNAME LIKE 'opinion%'
/*
OPINION.OPINIONCLASSNAMEINDEX read: 18481
*/
This query is very slow and not use index:
select count(*) from opinion where className not like 'opinion%';
4826 ms
SELECT
COUNT(*)
FROM PUBLIC.OPINION
/* PUBLIC.OPINION.tableScan */
/* scanCount: 1099380 */
WHERE NOT (CLASSNAME LIKE 'opinion%')
/*
total: 545475
OPINION.OPINION_DATA read: 545470 (99%)
overflow read: 5 (0%)
*/
Why NOT-LIKE is extremely slow? How I can improve it?
Best
Marcin M.
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