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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.
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@ -4392,7 +4392,7 @@ protected:
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/*
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All descendant classes have their send_data() skip the first
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unit->offset_limit_cnt rows sent. Select_materialize
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also uses unit->get_unit_column_types().
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also uses unit->get_column_types().
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*/
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SELECT_LEX_UNIT *unit;
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/* Something used only by the parser: */
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