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Bug #30377: EXPLAIN loses last_query_cost when used with UNION

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Currently the Last_query_cost session status variable shows
only the cost of a single flat subselect. For complex queries
(with subselects or unions etc) Last_query_cost is not valid
as it was showing the cost for the last optimized subselect.
Fixed by reseting to zero Last_query_cost when the complete
cost of the query cannot be determined.
Last_query_cost will be non-zero only for single flat queries.
This commit is contained in:
gkodinov/kgeorge@magare.gmz
2007-08-28 18:51:03 +03:00
parent 4446fd4b0d
commit cfaa0983c8
4 changed files with 108 additions and 2 deletions
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22
sql/sql_lex.h
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@ -1257,6 +1257,28 @@ typedef struct st_lex : public Query_tables_list
void reset_n_backup_query_tables_list(Query_tables_list *backup);
void restore_backup_query_tables_list(Query_tables_list *backup);
/**
@brief check if the statement is a single-level join
@return result of the check
@retval TRUE The statement doesn't contain subqueries, unions and
stored procedure calls.
@retval FALSE There are subqueries, UNIONs or stored procedure calls.
*/
bool is_single_level_stmt()
{
/*
This check exploits the fact that the last added to all_select_list is
on its top. So select_lex (as the first added) will be at the tail
of the list.
*/
if (&select_lex == all_selects_list && !sroutines.records)
{
DBUG_ASSERT(!all_selects_list->next_select_in_list());
return TRUE;
}
return FALSE;
}
} LEX;
struct st_lex_local: public st_lex