Question

我有以下查询：

SELECT table_1.id

FROM
table_1
LEFT JOIN table_2 ON (table_1.id = table_2.id)

WHERE
table_1.col_condition_1 = 0
AND table_1.col_condition_2 NOT IN (3, 4)
AND (table_2.id is NULL OR table_1.date_col > table_2.date_col)

LIMIT 5000;

我有以下键和索引：

table_1.id主键。
在table_1.col_condition_1上的索引
在table_1.col_condition_2上的索引
表_1.col_condition_1和表_1.col_condition_2上的复合索引

获取正确的索引。查询说明：

+--+----+-------------+---------+--------+---------------------------------------------------------------------+-----------------------+---------+------------+----------+-----------------------+--+
|  | id | select_type |  table  |  type  |                            possible_keys                            |          key          | key_len |    ref     |   rows   |         Extra         |  |
+--+----+-------------+---------+--------+---------------------------------------------------------------------+-----------------------+---------+------------+----------+-----------------------+--+
|  |  1 | SIMPLE      | table_1 | range  | "the composite index", col_condition_1 index ,col_condition_2 index | "the composite index" |       7 |            | 11819433 | Using index condition |  |
|  |  1 | SIMPLE      | table_2 | eq_ref | PRIMARY,id_UNIQUE                                                   | PRIMARY               |       8 | table_1.id |        1 | Using where           |  |
+--+----+-------------+---------+--------+---------------------------------------------------------------------+-----------------------+---------+------------+----------+-----------------------+--+

表_1拥有约60 MM记录，表_2具有约4 MM记录。

查询需要60秒才能返回结果。

有趣的是：

SELECT table_1.id

FROM
table_1
LEFT JOIN table_2 ON (table_1.id = table_2.id)

WHERE
table_1.col_condition_1 = 0
AND table_1.col_condition_2 NOT IN (3, 4)

LIMIT 5000;

花费145毫秒返回结果，并选择与第一个查询相同的索引。

SELECT table_1.id

FROM
table_1
LEFT JOIN table_2 ON (table_1.id = table_2.id)

WHERE
table_1.col_condition_1 = 0
AND (table_2.id is NULL OR table_1.date_col > table_2.date_col)

LIMIT 5000;

需要174毫秒才能返回结果。

查询说明：

+----+-------------+---------+--------+---------------------------------------------------------------------+-----------------+---------+------------+----------+-------------+
| id | select_type |  table  |  type  |                            possible_keys                            |       key       | key_len |    ref     |   rows   |    Extra    |
+----+-------------+---------+--------+---------------------------------------------------------------------+-----------------+---------+------------+----------+-------------+
|  1 | SIMPLE      | table_1 | ref    | "the composite index", col_condition_1 index ,col_condition_2 index | col_condition_1 |       2 | const      | 30381842 | NULL        |
|  1 | SIMPLE      | table_2 | eq_ref | PRIMARY,id_UNIQUE                                                   | PRIMARY         |       8 | table_1.id |        1 | Using where |
+----+-------------+---------+--------+---------------------------------------------------------------------+-----------------+---------+------------+----------+-------------+

和

SELECT table_1.id

FROM
table_1
LEFT JOIN table_2 ON (table_1.id = table_2.id)

WHERE
table_1.col_condition_2 NOT IN (3, 4)
AND (table_2.id is NULL OR table_1.date_col > table_2.date_col)

LIMIT 5000;

大约需要1秒才能返回结果。

查询说明：

+----+-------------+---------+--------+---------------------------------------------------------------------+-----------------+---------+------------+----------+-----------------------+
| id | select_type |  table  |  type  |                            possible_keys                            |       key       | key_len |    ref     |   rows   |         Extra         |
+----+-------------+---------+--------+---------------------------------------------------------------------+-----------------+---------+------------+----------+-----------------------+
|  1 | SIMPLE      | table_1 | range  | "the composite index", col_condition_1 index ,col_condition_2 index | col_condition_2 |       5 |            | 36254294 | Using index condition |
|  1 | SIMPLE      | table_2 | eq_ref | PRIMARY,id_UNIQUE                                                   | PRIMARY         |       8 | table_1.id |        1 | Using where           |
+----+-------------+---------+--------+---------------------------------------------------------------------+-----------------+---------+------------+----------+-----------------------+

另外，当我分别使用每个where条件时，查询会在约100毫秒内返回结果。

我的问题是，即使同时使用正确的索引并使用任意两个条件执行查询，为什么在同时使用三个where条件时查询要花大量时间（60秒）才能返回结果三个条件也可以在更短的时间内返回结果。

还有，有没有一种方法可以优化此查询？

谢谢。

编辑：

创建表：

表_1：

CREATE TABLE `table_1` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `col_condition_1` tinyint(1) DEFAULT '0',
  `col_condition_2` int(11) DEFAULT NULL,
  `date_col` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`),
  KEY `compositeidx` (`col_condition_1`,`col_condition_2`),
  KEY `col_condition_1_idx` (`col_condition_1`),
  KEY `col_condition_2_idx` (`col_condition_2`)
) ENGINE=InnoDB AUTO_INCREMENT=68272192 DEFAULT CHARSET=utf8

表_2：

CREATE TABLE `table_2` (
  `id` bigint(20) NOT NULL,
  `date_col` timestamp NULL DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `id_UNIQUE` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1

选择条件较慢的三个查询，但条件三个较快的三个查询的任意组合的同一查询

0 个答案: