Fixed bug mdev-11745.

Due to this bug many queries that contained a window function
with MIN/MAX aggregation returned wrong results.

Calculation of a MIN/MAX aggregate function uses cache objects
and a comparator object that are created and set up in
Item_sum_hybrid::fix_fields () by a call of Item_sum_hybrid::setup_hybrid().
The latter binds the objects to the first argument of the
MIN/MAX function. Meanwhile window function perform aggregation
over fields of a temporary table. So binding must be done rather to
these fields. The earliest moment when setup the objects used in
MIN/max functions can be done is after all calls of the method
split_sum_func().

This patch introduces this late setup, but only for aggregate
functions used in window functions.
Probably it makes sense to use this late setup for all MIN/MAX
objects.

1 files changed, 2 insertions, 1 deletions

diff --git a/sql/item_sum.cc b/sql/item_sum.cc
index 2ca1be31ae1..098b1ea8750 100644
--- a/sql/item_sum.cc
+++ b/sql/item_sum.cc
@@ -1161,7 +1161,8 @@ Item_sum_hybrid::fix_fields(THD *thd, Item **ref)
   case TIME_RESULT:
     DBUG_ASSERT(0);
   };
-  setup_hybrid(thd, args[0], NULL);
+  if (!is_window_func_sum_expr())
+    setup_hybrid(thd, args[0], NULL);
   /* MIN/MAX can return NULL for empty set indepedent of the used column */
   maybe_null= 1;
   result_field=0;