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, 3 insertions, 0 deletions

diff --git a/sql/item_sum.h b/sql/item_sum.h
index a838bd0bc10..57375b29114 100644
--- a/sql/item_sum.h
+++ b/sql/item_sum.h
@@ -576,6 +576,8 @@ public:
   bool check_vcol_func_processor(void *arg);
   virtual void setup_window_func(THD *thd, Window_spec *window_spec) {}
   void mark_as_window_func_sum_expr() { window_func_sum_expr_flag= true; }
+  bool is_window_func_sum_expr() { return window_func_sum_expr_flag; }
+  virtual void setup_caches(THD *thd) {};
 };
 
 
@@ -1053,6 +1055,7 @@ protected:
   void no_rows_in_result();
   void restore_to_before_no_rows_in_result();
   Field *create_tmp_field(bool group, TABLE *table);
+  void setup_caches(THD *thd) { setup_hybrid(thd, arguments()[0], NULL); }
 };