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MDEV-38877: Unnecessary filesort on derived table materialization #4722

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MDEV-38877: Unnecessary filesort on derived table materialization #4722

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32 changes: 32 additions & 0 deletions mysql-test/main/mdev-38877.result
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Original file line number Diff line number Diff line change
@@ -0,0 +1,32 @@
#
# MDEV-38877: Unnecessary filesort on derived table materialization
# when derived table is inherently sorted by the grouping columns
#
CREATE TABLE t1 (
groups_20 int NOT NULL,
groups_20_2 int NOT NULL,
b int,
PRIMARY KEY (groups_20, groups_20_2)
);
CREATE TABLE t2 (a int, b int, index(a));
INSERT INTO t1 SELECT seq/1000, seq+1, seq from seq_1_to_10000;
INSERT INTO t2 SELECT seq, seq from seq_1_to_1000;
ANALYZE TABLE t1, t2;
EXPLAIN
SELECT
a,
SUM(b)
FROM (
SELECT
groups_20
FROM t1
GROUP BY groups_20
HAVING COUNT(*) != 1000
) DT
JOIN t2 ON a = groups_20
GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t2 ALL a NULL NULL NULL 1000 Using where; Using temporary; Using filesort
1 PRIMARY <derived2> ref key0 key0 4 test.t2.a 1
2 DERIVED t1 index PRIMARY PRIMARY 8 NULL 10000 Using index
DROP TABLE t1, t2;
39 changes: 39 additions & 0 deletions mysql-test/main/mdev-38877.test
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--source include/have_sequence.inc

--echo #
--echo # MDEV-38877: Unnecessary filesort on derived table materialization
--echo # when derived table is inherently sorted by the grouping columns
--echo #

CREATE TABLE t1 (
groups_20 int NOT NULL,
groups_20_2 int NOT NULL,
b int,
PRIMARY KEY (groups_20, groups_20_2)
);

CREATE TABLE t2 (a int, b int, index(a));

--disable_result_log
INSERT INTO t1 SELECT seq/1000, seq+1, seq from seq_1_to_10000;

INSERT INTO t2 SELECT seq, seq from seq_1_to_1000;

ANALYZE TABLE t1, t2;
--enable_result_log

EXPLAIN
SELECT
a,
SUM(b)
FROM (
SELECT
groups_20
FROM t1
GROUP BY groups_20
HAVING COUNT(*) != 1000
) DT
JOIN t2 ON a = groups_20
GROUP BY a;

DROP TABLE t1, t2;
17 changes: 15 additions & 2 deletions sql/sql_select.cc
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Expand Up @@ -7916,7 +7916,21 @@ bool sort_and_filter_keyuse(JOIN *join, DYNAMIC_ARRAY *keyuse,
{
if (!(use->used_tables & ~OUTER_REF_TABLE_BIT) &&
use->optimize != KEY_OPTIMIZE_REF_OR_NULL)
use->table->const_key_parts[use->key]|= use->keypart_map;
{
TABLE_LIST *derived_table= use->table->pos_in_table_list;
if (derived_table && derived_table->select_lex)
{
st_select_lex_unit *master_unit=
derived_table->select_lex->master_unit();
if (master_unit)
derived_table= master_unit->derived;
}
// derived tables shouldn't treat outer
// references as constants
if (!(derived_table && derived_table->is_materialized_derived()) ||
use->used_tables == 0)
use->table->const_key_parts[use->key]|= use->keypart_map;
}
if (use->keypart != FT_KEYPART)
{
if (use->key == prev->key && use->table == prev->table)
Expand Down Expand Up @@ -27562,7 +27576,6 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
*fatal_error= false;
/* Check that we are always called with first non-const table */
DBUG_ASSERT(tab == tab->join->join_tab + tab->join->const_tables);

/* Sorting a single row can always be skipped */
if (tab->type == JT_EQ_REF ||
tab->type == JT_CONST ||
Expand Down
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