MDEV-16917 Index affects query results

The optimizer erroneously allowed to use join cache when joining a
splittable materialized table together with splitting optimization.
As a consequence in some rare cases the server returned wrong result
sets for queries with materialized derived.

This patch allows to use either join cache without usage of splitting
technique for materialization of a splittable derived table or splitting
without usage of join cache when joining such table. The costs the these
alternatives are compared and the best variant is chosen.

1 files changed, 7 insertions, 0 deletions

diff --git a/sql/opt_split.cc b/sql/opt_split.cc
index 611e70376c8..c5e31ba5bcf 100644
--- a/sql/opt_split.cc
+++ b/sql/opt_split.cc
@@ -267,6 +267,13 @@ void TABLE::deny_splitting()
 }
 
 
+double TABLE::get_materialization_cost()
+{
+  DBUG_ASSERT(spl_opt_info != NULL);
+  return spl_opt_info->unsplit_cost;
+}
+
+
 /* This structure is auxiliary and used only in the function that follows it */
 struct SplM_field_ext_info: public SplM_field_info
 {