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.

3 files changed, 6 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;
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); }
 };
 
 
diff --git a/sql/item_windowfunc.cc b/sql/item_windowfunc.cc
index a13967eaaad..fb2ad666018 100644
--- a/sql/item_windowfunc.cc
+++ b/sql/item_windowfunc.cc
@@ -150,6 +150,7 @@ void Item_window_func::split_sum_func(THD *thd, Ref_ptr_array ref_pointer_array,
     Item **p_item= &window_func()->arguments()[i];
     (*p_item)->split_sum_func2(thd, ref_pointer_array, fields, p_item, flags);
   }
+  window_func()->setup_caches(thd);
 }