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MWL#90: Address review feedback part #19: More comments

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This commit is contained in:
Sergey Petrunya 2011-04-05 14:33:15 +04:00
parent 151207134b
commit 81c6f73ff2
1 changed files with 28 additions and 2 deletions
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30
sql/opt_subselect.cc
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@ -364,11 +364,14 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
(Subquery is correlated to the immediate outer query &&
Subquery !contains {GROUP BY, ORDER BY [LIMIT],
aggregate functions}) && subquery predicate is not under "NOT IN"))
6. No execution method was already chosen (by a prepared statement).
(*) The subquery must be part of a SELECT statement. The current
condition also excludes multi-table update statements.
A note about prepared statements: we want the if-branch to be taken on
PREPARE and each EXECUTE. The rewrites are only done once, but we need
join->sj_subselects list to be populated for every EXECUTE.
Determine whether we will perform subquery materialization before
calling the IN=>EXISTS transformation, so that we know whether to
perform the whole transformation or only that part of it which wraps
@ -534,6 +537,20 @@ bool make_in_exists_conversion(THD *thd, JOIN *join, Item_in_subselect *item)
DBUG_ENTER("make_in_exists_conversion");
JOIN *child_join= item->unit->first_select()->join;
Item_subselect::trans_res res;
/*
We're going to finalize IN->EXISTS conversion.
Normally, IN->EXISTS conversion takes place inside the
Item_subselect::fix_fields() call, where item_subselect->fixed==FALSE (as
fix_fields() haven't finished yet) and item_subselect->changed==FALSE (as
the conversion haven't been finalized)
At the end of Item_subselect::fix_fields() we had to set fixed=TRUE,
changed=TRUE (the only other option would have been to return error).
So, now we have to set these back for the duration of select_transformer()
call.
*/
item->changed= 0;
item->fixed= 0;
@ -566,6 +583,10 @@ bool make_in_exists_conversion(THD *thd, JOIN *join, Item_in_subselect *item)
DBUG_RETURN(TRUE);
item->substitution= NULL;
/*
If this is a prepared statement, repeat the above operation for
prep_where (or prep_on_expr).
*/
if (!thd->stmt_arena->is_conventional())
{
tree= (item->emb_on_expr_nest == (TABLE_LIST*)NO_JOIN_NEST)?
@ -752,7 +773,12 @@ skip_conversion:
do_fix_fields))
DBUG_RETURN(TRUE);
(*in_subq)->substitution= NULL;
/*
If this is a prepared statement, repeat the above operation for
prep_where (or prep_on_expr). Subquery-to-semijoin conversion is
done once for prepared statement.
*/
if (!thd->stmt_arena->is_conventional())
{
tree= ((*in_subq)->emb_on_expr_nest == NO_JOIN_NEST)?