Question bête... Count(1) ou count(*) ?

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Envoyé par SheikYerbouti

Cela n'est-il pas simplement du à l'existence d'une clause Where commune ?

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Non, c'est grâce à l'optimalisation de "count".

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select count (a) from t1 where x <= 501; select count (x) from t1 where x <= 502; select count (1) from t1 where x <= 503; select count (b) from t1 where x <= 504;

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(cursor_sharing=EXACT)

tu peux essayer avec un count(d) pour voir ?

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Envoyé par McM

tu peux essayer avec un count(d) pour voir ?

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select count (b) from t1 where x <= 504;   -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 4 | 2 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 4 | | | |* 2 | INDEX RANGE SCAN| T1X | 504 | 2016 | 2 (0)| 00:00:01 | --------------------------------------------------------------------------   2 - access("X"<=504)

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select count (d) from t1 where x <= 504;   ------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 4005 | 507 (0)| 00:00:07 | | 1 | SORT AGGREGATE | | 1 | 4005 | | | | 2 | TABLE ACCESS BY INDEX ROWID| T1 | 504 | 1971K| 507 (0)| 00:00:07 | |* 3 | INDEX RANGE SCAN | T1X | 504 | | 2 (0)| 00:00:01 | -------------------------------------------------------------------------------------   3 - access("X"<=504)

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select count (d) from t1 where x <= 5000;   --------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 4005 | 4400 (1)| 00:00:53 | | 1 | SORT AGGREGATE | | 1 | 4005 | | | |* 2 | TABLE ACCESS FULL| T1 | 5000 | 19M| 4400 (1)| 00:00:53 | ---------------------------------------------------------------------------   2 - filter("X"<=5000)

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pour info : http://asktom.oracle.com/pls/asktom/...:1156151916789 :)