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Fixed bug mdev-11081.

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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.
This commit is contained in:
Igor Babaev
2016-11-21 10:33:06 -08:00
parent 022aeda4c0
commit 665045f985
8 changed files with 92 additions and 10 deletions
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2
sql/sql_cursor.cc
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@ -433,7 +433,7 @@ void Materialized_cursor::on_table_fill_finished()
bool Select_materialize::send_result_set_metadata(List<Item> &list, uint flags)
{
DBUG_ASSERT(table == 0);
if (create_result_table(unit->thd, unit->get_unit_column_types(),
if (create_result_table(unit->thd, unit->get_column_types(true),
FALSE,
thd->variables.option_bits | TMP_TABLE_ALL_COLUMNS,
"", FALSE, TRUE, TRUE))