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author | unknown <timour@askmonty.org> | 2012-06-06 22:26:40 +0300 |
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committer | unknown <timour@askmonty.org> | 2012-06-06 22:26:40 +0300 |
commit | c2677de7aca09a0ba4b680b5227bda3865ab9290 (patch) | |
tree | 980157e9eaf1062641572da371d1ae7fcc371625 /sql/item.h | |
parent | 8efc63ba5d32b77501226921ee503b9ae513a365 (diff) | |
parent | 7ddd5418d01e60dba2ae69a668e7c9f811613451 (diff) | |
download | mariadb-git-c2677de7aca09a0ba4b680b5227bda3865ab9290.tar.gz |
Merge the fix for lp:944706, mdev-193
Diffstat (limited to 'sql/item.h')
-rw-r--r-- | sql/item.h | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/sql/item.h b/sql/item.h index a9c1153d236..f7f3edda384 100644 --- a/sql/item.h +++ b/sql/item.h @@ -1395,21 +1395,21 @@ public: { return cmp_context == IMPOSSIBLE_RESULT || item->cmp_context == cmp_context; } - /* + /** Test whether an expression is expensive to compute. Used during optimization to avoid computing expensive expressions during this phase. Also used to force temp tables when sorting on expensive functions. - TODO: + @todo Normally we should have a method: cost Item::execution_cost(), where 'cost' is either 'double' or some structure of various cost parameters. - NOTE - This function is now used to prevent evaluation of materialized IN - subquery predicates before it is allowed. grep for - DontEvaluateMaterializedSubqueryTooEarly to see the uses. + @note + This function is now used to prevent evaluation of expensive subquery + predicates during the optimization phase. It also prevents evaluation + of predicates that are not computable at this moment. */ virtual bool is_expensive() { |