MySQL派生表(derived)优化一例

1、什么是派生表derived

关键字：子查询–>在From后where前的子查询

mysql> explain select *  from (select *  from t) a where id=2;
+----+-------------+------------+------+---------------+-------------+---------+-------+------+-------+
| id | select_type | table      | type | possible_keys | key         | key_len | ref   | rows | Extra |
+----+-------------+------------+------+---------------+-------------+---------+-------+------+-------+
|  1 | PRIMARY     | <derived2> | ref  | <auto_key0>   | <auto_key0> | 4       | const |    0 | NULL  |
|  2 | DERIVED     | t          | ALL  | NULL          | NULL        | NULL    | NULL  |    4 | NULL  |
+----+-------------+------------+------+---------------+-------------+---------+-------+------+-------+

MySQL 5.7开始优化器引入derived_merge，可以理解为Oracle的子查询展开，有优化器参数optimizer_switch='derived_merge=ON’来控制，默认为打开。

但是仍然有很多限制，当派生子查询存在以下操作时该特性无法生效：UNION 、GROUP BY、DISTINCT、LIMIT/OFFSET以及聚合操作

2、派生表SQL优化一例

mysql> select @@version;
+------------+
| @@version  |
+------------+
| 5.6.16-log |
+------------+

SELECT A.*, b.vendor_name, c.chinese_name, c.english_name, d.name AS category_name, e.value, a.season_code
  FROM PR_XXX A
  LEFT JOIN VXX B
    ON A.VENDOR_ID = B.VENDOR_ID
  LEFT JOIN BXX C
    ON A.BRAND_ID = C.BRAND_ID
  LEFT JOIN CXX D
    ON A.CATEGORY_ID = D.CATEGORY_ID
  LEFT JOIN PXX E
    ON A.PRODUCT_ID = E.PRODUCT_ID
 INNER JOIN (SELECT SS.PRODUCT_ID
               FROM SKU_XXX SS
              WHERE SS.ENABLED = 1
              GROUP BY SS.PRODUCT_ID
             HAVING SUM(SS.STORE) >= 1) ST
    ON ST.PRODUCT_ID = A.PRODUCT_ID
 WHERE A.vendor_id = 91011
   AND A.enabled = 1
   AND A.status = ''
   AND a.season_code = ''
   AND 1 = 1
   AND a.brand_id = ''
   AND E.KEY_NAME = 'XXX'
 ORDER BY product_id LIMIT 0, 10

执行计划如下

++----+-------------+------------+-------------+----------------------------------------------------------------+-----------------------------------+---------+--------------------------+---------+---------------------------------------------------------------------------------+----+--
| id | select_type | table      | type        | possible_keys                                                  | key                               | key_len | ref                      | rows    | Extra                                                                           |
+----+-------------+------------+-------------+----------------------------------------------------------------+-----------------------------------+---------+--------------------------+---------+---------------------------------------------------------------------------------+
|  1 | PRIMARY     | A          | index_merge | PRIMARY,vendor_id,IDX_VENDOR_ID_STATUS,IDX_BRAND_ID,IDX_STATUS | IDX_VENDOR_ID_STATUS,IDX_BRAND_ID | 9,8     | NULL                     |       5 | Using intersect(IDX_VENDOR_ID_STATUS,IDX_BRAND_ID); Using where; Using filesort |
|  1 | PRIMARY     | B          | const       | PRIMARY                                                        | PRIMARY                           | 8       | const                    |       1 | NULL                                                                            |
|  1 | PRIMARY     | C          | const       | PRIMARY                                                        | PRIMARY                           | 8       | const                    |       1 | Using where                                                                     |
|  1 | PRIMARY     | D          | eq_ref      | PRIMARY                                                        | PRIMARY                           | 8       | ger-prd-db.A.category_id |       1 | NULL                                                                            |
|  1 | PRIMARY     | E          | ref         | IDX_PRODUCT_PROPERTY_PRODUCT_ID                                | IDX_PRODUCT_PROPERTY_PRODUCT_ID   | 8       | ger-prd-db.A.product_id  |       3 | Using where                                                                     |
|  1 | PRIMARY     | <derived2> | ref         | <auto_key0>                                                    | <auto_key0>                       | 9       | ger-prd-db.A.product_id  |      10 | Using index                                                                     |
|  2 | DERIVED     | SS         | index       | IDX_PRODUCT_ID                                                 | IDX_PRODUCT_ID                    | 9       | NULL                     | 1715829 | Using where                                                                     |
+----+-------------+------------+-------------+----------------------------------------------------------------+-----------------------------------+---------+--------------------------+---------+---------------------------------------------------------------------------------+

关键表索引信息

mysql> show index  from PR_XXX ;
+---------+------------+-------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table   | Non_unique | Key_name                | Seq_in_index | Column_name  | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+---------+------------+-------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| PR_XXX  |          0 | PRIMARY                 |            1 | product_id   | A         |      283783 |     NULL | NULL   |      | BTREE      |         |               |
| PR_XXX  |          0 | vendor_id               |            1 | vendor_id    | A         |          92 |     NULL | NULL   |      | BTREE      |         |               |
| PR_XXX  |          0 | vendor_id               |            2 | product_code | A         |      283783 |     NULL | NULL   |      | BTREE      |         |               |
| PR_XXX  |          1 | IDX_VENDOR_ID_STATUS    |            1 | vendor_id    | A         |          82 |     NULL | NULL   |      | BTREE      |         |               |
| PR_XXX  |          1 | IDX_VENDOR_ID_STATUS    |            2 | status       | A         |         392 |     NULL | NULL   |      | BTREE      |         |               |
| PR_XXX  |          1 | IDX_BRAND_ID            |            1 | brand_id     | A         |        2866 |     NULL | NULL   |      | BTREE      |         |               |
| PR_XXX  |          1 | IDX_STATUS              |            1 | status       | A         |          10 |     NULL | NULL   |      | BTREE      |         |               |
| PR_XXX  |          1 | IDX_PRODUCT_CATEGORY_ID |            1 | category_id  | A         |         276 |     NULL | NULL   |      | BTREE      |         |               |
| PR_XXX  |          1 | IDX_SPU_ID              |            1 | spu_id       | A         |      283783 |     NULL | NULL   | YES  | BTREE      |         |               |
+---------+------------+-------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
9 rows in set (0.00 sec)
mysql> show index from SKU_XXX;
+-----------+------------+----------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table     | Non_unique | Key_name       | Seq_in_index | Column_name  | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-----------+------------+----------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| SKU_XXX   |          0 | PRIMARY        |            1 | sku_store_id | A         |     1715829 |     NULL | NULL   |      | BTREE      |         |               |
| SKU_XXX   |          1 | IDX_SKU_ID     |            1 | sku_id       | A         |     1715829 |     NULL | NULL   | YES  | BTREE      |         |               |
| SKU_XXX   |          1 | IDX_PRODUCT_ID |            1 | product_id   | A         |      857914 |     NULL | NULL   | YES  | BTREE      |         |               |
+-----------+------------+----------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

建议进行SQL改写

SELECT A.*, b.vendor_name, c.chinese_name, c.english_name, d.name as category_name, e.value, a.season_code
   FROM PR_XXX A
   LEFT JOIN VXX B
     ON A.VENDOR_ID = B.VENDOR_ID
   LEFT JOIN BXX C
     ON A.BRAND_ID = C.BRAND_ID
   LEFT JOIN CXX D
     ON A.CATEGORY_ID = D.CATEGORY_ID
   LEFT JOIN PXX E
     ON A.PRODUCT_ID = E.PRODUCT_ID
  INNER JOIN SKU_XXX SS
     ON SS.ENABLED = 1
    and SS.PRODUCT_ID = A.PRODUCT_ID
  where  A.vendor_id = 20
   AND A.enabled = 1
   AND A.status = ''
   AND a.season_code = '18SS'
   AND 1 = 1
   AND a.brand_id = ''
    AND E.KEY_NAME = 'BrandID'
   and  SS.ENABLED = 1
  GROUP BY a.PRODUCT_ID
 having SUM(SS.STORE) >= 1
  ORDER BY a.product_id limit 0, 10;

改写后的执行计划

+----+-------------+-------+-------------+----------------------------------------+-----------------------------------+---------+--------------------------+------+--------------------------------------------------------------------------------------------------+
| id | select_type | table | type        | possible_keys                          | key                               | key_len | ref                      | rows | Extra                                                                                            |
+----+-------------+-------+-------------+----------------------------------------+-----------------------------------+---------+--------------------------+------+--------------------------------------------------------------------------------------------------+
|  1 | SIMPLE      | A     | index_merge | PRIMARY,vendor_id,....................,| IDX_VENDOR_ID_STATUS,IDX_BRAND_ID | 9,8     | NULL                     |    5 | Using intersect(IDX_VENDOR_ID_STATUS,IDX_BRAND_ID); Using where; Using temporary; Using filesort |
|  1 | SIMPLE      | B     | const       | PRIMARY                                | PRIMARY                           | 8       | const                    |    1 | NULL                                                                                             |
|  1 | SIMPLE      | C     | const       | PRIMARY                                | PRIMARY                           | 8       | const                    |    1 | Using where                                                                                      |
|  1 | SIMPLE      | D     | eq_ref      | PRIMARY                                | PRIMARY                           | 8       | ger-prd-db.A.category_id |    1 | NULL                                                                                             |
|  1 | SIMPLE      | SS    | ref         | IDX_PRODUCT_ID                         | IDX_PRODUCT_ID                    | 9       | ger-prd-db.A.product_id  |    2 | Using where                                                                                      |
|  1 | SIMPLE      | E     | ref         | IDX_PRODUCT_PROPERTY_PRODUCT_ID        | IDX_PRODUCT_PROPERTY_PRODUCT_ID   | 8       | ger-prd-db.A.product_id  |    3 | Using where                                                                                      |
+----+-------------+-------+-------------+----------------------------------------+-----------------------------------+---------+--------------------------+------+--------------------------------------------------------------------------------------------------+

优化前：2 rows in set (2.12 sec)
优化后：2 rows in set (0.00 sec)