Fixed bug mdev-11081.

The idea of this fix was taken from the patch by Roy Lyseng
for mysql-5.6 bug iBug#14740889: "Wrong result for aggregate
functions when executing query through cursor".

Here's Roy's comment for his patch:
"
The problem was that a grouped query did not behave properly when
executed using a cursor. On further inspection, the query used one
intermediate temporary table for the grouping.
Then, Select_materialize::send_result_set_metadata created a temporary
table for storing the query result. Notice that get_unit_column_types()
is used to retrieve column meta-data for the query. The items contained
in this list are later modified so that their result_field points to
the row buffer of the materialized temporary table for the cursor.
But prior to this, these result_field objects have been prepared for
use in the grouping operation, by JOIN::make_tmp_tables_info(), hence
the grouping operation operates on wrong column buffers.

The problem is solved by using the list JOIN::fields when copying data
to the materialized table. This list is set by JOIN::make_tmp_tables_info()
and points to the columns of the last intermediate temporary table of
the executed query. For a UNION, it points to the temporary table
that is the result of the UNION query.

Notice that we have to assign a value to ::fields early in JOIN::optimize()
in case the optimization shortcuts due to a const plan detection.

A more optimal solution might be to avoid creating the final temporary
table when the query result is already stored in a temporary table.
"
The patch does not contain a test case, but the description of the
problem corresponds exactly what could be observed in the test
case for mdev-11081.

1 files changed, 1 insertions, 1 deletions

diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc
index 21c633333f1..e90efbd82be 100644
--- a/sql/item_subselect.cc
+++ b/sql/item_subselect.cc
@@ -4572,7 +4572,7 @@ subselect_hash_sj_engine::get_strategy_using_schema()
     return COMPLETE_MATCH;
   else
   {
-    List_iterator<Item> inner_col_it(*item_in->unit->get_unit_column_types());
+    List_iterator<Item> inner_col_it(*item_in->unit->get_column_types(false));
     Item *outer_col, *inner_col;
 
     for (uint i= 0; i < item_in->left_expr->cols(); i++)