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, 1 insertions, 0 deletions

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);
 }