We earlier leveraged the server functionality provided by
Item_in_subselect::create_in_to_exists_cond and
Item_in_subselect::inject_in_to_exists_cond
to create and inject the in-to-exists predicate into an IN
subquery's JOIN struct. With this patch, we leave the IN subquery's
JOIN unaltered and instead directly perform this predicate creation
and injection into ColumnStore's select execution plan.
Original SH implementation sends the result set back to the client
thus it can't be used in INSERT..SELECT, SELECT INTO OUTFILE,CREATE
TABLE AS SELECT etc.
CLX-77 feature has been backported into MDB to enable SH to run
query part of the mentioned queries.
This happens in external_lock() whilst locking the table.
Fixes LIMIT=1 optimization for EXISTS_SUBS subqueries.
external_lock() contains if condition that gives false positive
for SH + pushed conditions.
external_lock() now resets in_subquery_conversion_threshold
variable that governs IN_INTO_SUBQUERY optimization for
queries run in table mode.
external_lock() now purges dynamicall allocated condInfo for
SH and DH execution path.
Commented out UNION check b/c if condition gives false positives
and silently enables table mode execution for queries w/o
UNION.
