diff options
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 b3801e6c488..df220118745 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() { |