PolarDB:Convert IN predicates into joins

Prerequisites

• A cluster of PolarDB for MySQL 8.0 whose revision version is 8.0.2.2.10 or later. For information about how to view the cluster version, see Engine versions 5.6, 5.7, and 8.0.

• The number of elements in the IN list reaches the number specified in the loose_in_predicate_conversion_threshold parameter.

• The [NOT]IN condition is at the top level of the WHERE or ON clause.

Usage

You can use the loose_in_predicate_conversion_threshold parameter to specify whether to enable the feature. For more information, see Specify cluster and node parameters.

Examples

Original query:

mysql> EXPLAIN  SELECT * FROM t WHERE a IN (1,2,3,5,5);
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | t     | NULL       | ALL  | NULL          | NULL | NULL    | NULL |  160 |    50.00 | Using where |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)
mysql> EXPLAIN format=tree SELECT * FROM t WHERE a IN (1,2,3,5,5);
+------------------------------------------------------------------------------------------------------+
| EXPLAIN                                                                                              |
+------------------------------------------------------------------------------------------------------+
| -> Filter: (t.a IN (1,2,3,5,5))  (cost=16.25 rows=80)
    -> TABLE scan ON t  (cost=16.25 rows=160)
 |
+------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

Converted query:

mysql> SET in_predicate_conversion_threshold=5;
mysql> EXPLAIN  SELECT * FROM t WHERE a IN (1,2,3,5,5);
+----+-------------+------------+------------+--------+---------------------+---------------------+---------+----------+------+----------+--------------------------+
| id | select_type | table      | partitions | type   | possible_keys       | key                 | key_len | ref      | rows | filtered | Extra                    |
+----+-------------+------------+------------+--------+---------------------+---------------------+---------+----------+------+----------+--------------------------+
|  1 | PRIMARY     | t          | NULL       | ALL    | NULL                | NULL                | NULL    | NULL     |  160 |   100.00 | Using where              |
|  1 | PRIMARY     | <derived3> | NULL       | eq_ref | <auto_distinct_key> | <auto_distinct_key> | 8       | test.t.a |    1 |   100.00 | Using where; Using index |
|  3 | DERIVED     | NULL       | NULL       | NULL   | NULL                | NULL                | NULL    | NULL     | NULL |     NULL | IN-list Converted        |
+----+-------------+------------+------------+--------+---------------------+---------------------+---------+----------+------+----------+--------------------------+
mysql> EXPLAIN format=tree SELECT * FROM t1 WHERE a IN (1,2,3,5,5);
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN                                                                                                                                                                                                                                                                                                    |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| -> Nested loop semijoin
    -> Filter: (t1.a IS NOT NULL)  (cost=0.55 rows=3)
        -> TABLE scan ON t1  (cost=0.55 rows=3)
    -> Filter: (t1.a = tvc_0._col_1)
        -> Index lookup ON tvc_0 using <auto_key0> (_col_1=t1.a)
            -> Materialize
                -> scan ON in-list: 5 rows