Fixed the bug mdev-12673.

This patch corrects the fix for the bug mdev-10693.
It is critical for the function get_best_combination() not to call
create_ref_for_key() for constant tables.
This bug could manifest itself only in multi-table subqueries where
one of the tables is accessed by a constant primary key.

1 files changed, 7 insertions, 5 deletions

diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index c5f2a83fc01..09e6ece7807 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -7844,12 +7844,14 @@ get_best_combination(JOIN *join)
   {
     if (j->bush_children)
       j= j->bush_children->start;
-      
+    
     used_tables|= j->table->map;
-    if ((keyuse= join->best_positions[tablenr].key) &&
-        create_ref_for_key(join, j, keyuse, TRUE, used_tables))
-     DBUG_RETURN(TRUE);              // Something went wrong
-
+    if (j->type != JT_CONST && j->type != JT_SYSTEM)
+    {
+      if ((keyuse= join->best_positions[tablenr].key) &&
+          create_ref_for_key(join, j, keyuse, TRUE, used_tables))
+        DBUG_RETURN(TRUE);              // Something went wrong
+    }
     if (j->last_leaf_in_bush)
       j= j->bush_root_tab;
   }