Fix bug lp:806943

Analysis:
This bug is yet another incarnation of the generic problem
where optimization of the outer query triggers evaluation
of a subquery, and this evaluation performs a destructive
change to the subquery plan. Specifically a temp table is
created for the DISTINCT operation that replaces the
original subquery table. Later, select_describe() attempts
to print the table name, however, there is no corresponding
TABLE_LIST object to the internal temp table, so we get a
crash. Execution works fine because it is not interested in
the corresponding TABLE_LIST object (or its name).

Solution:
Similar to other such bugs, block the evaluation of expensive
Items in convert_const_to_int().

1 files changed, 1 insertions, 1 deletions

diff --git a/sql/item_cmpfunc.cc b/sql/item_cmpfunc.cc
index dc25cf5942c..346ae243196 100644
--- a/sql/item_cmpfunc.cc
+++ b/sql/item_cmpfunc.cc
@@ -434,7 +434,7 @@ static bool convert_const_to_int(THD *thd, Item_field *field_item,
       field_item->field_type() != MYSQL_TYPE_YEAR)
     return 1;
 
-  if ((*item)->const_item())
+  if ((*item)->const_item() && !(*item)->is_expensive())
   {
     TABLE *table= field->table;
     ulong orig_sql_mode= thd->variables.sql_mode;