应用错误收集

我有一个带有主键的Job表和几个与日期相关的字段......

 +------------------+---------------+------+-----+-------------------+----------------+
| Field            | Type          | Null | Key | Default           | Extra          |
+------------------+---------------+------+-----+-------------------+----------------+
| jobId            | bigint(20)    | NO   | PRI | NULL              | auto_increment |
| creationDateTime | datetime      | NO   | MUL | NULL              |                |
| lastModified     | timestamp     | NO   | MUL | CURRENT_TIMESTAMP |                |
+------------------+---------------+------+-----+-------------------+----------------+

此表有426,579行和以下索引

+---------+------------+--------------------------+--------------+------------------+-----------+-------------+----------+--------+------+------------+---------+
| Table   | Non_unique | Key_name                 | Seq_in_index | Column_name      | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+---------+------------+--------------------------+--------------+------------------+-----------+-------------+----------+--------+------+------------+---------+
| Job     |          0 | PRIMARY                  |            1 | jobId            | A         |      439957 |     NULL | NULL   |      | BTREE      |         |
| Job     |          1 | Job_lastModified_idx     |            1 | lastModified     | A         |      439957 |     NULL | NULL   |      | BTREE      |         |
| Job     |          1 | Job_creationDateTime_idx |            1 | creationDateTime | A         |      439957 |     NULL | NULL   |      | BTREE      |         |
+---------+------------+--------------------------+--------------+------------------+-----------+-------------+----------+--------+------+------------+---------+

现在是一个查询，例如......

select * from Job
 where jobId > 1000
 and creationDateTime between '2011-09-07 18:29:24' and '2011-09-07 20:00:33';

按预期运行非常快（0s）

解释......

+----+-------------+-------+-------+----------------------------------+--------------------------+---------+------+------+-------------+
| id | select_type | table | type  | possible_keys                    | key                      | key_len | ref  | rows | Extra       |
+----+-------------+-------+-------+----------------------------------+--------------------------+---------+------+------+-------------+
|  1 | SIMPLE      | Job   | range | PRIMARY,Job_creationDateTime_idx | Job_creationDateTime_idx | 8       | NULL |   39 | Using where |
+----+-------------+-------+-------+----------------------------------+--------------------------+---------+------+------+-------------+

我看到针对lastmodified而不是creationDateTime

的等效查询的速度相同

然而稍微复杂的查询......

select * from Job
 where jobId > 1000
 and (lastModified between '2011-09-07 18:29:24' and '2011-09-07 20:00:33' 
      or creationDateTime between '2011-09-07 18:29:24' and '2011-09-07 20:00:33');

运行缓慢（9秒）并且由于某种原因最终不得不进行更大的扫描，即使如此按预期，它返回相同的行数（40）

+----+-------------+-------+-------+-------------------------------------------------------+---------+---------+------+--------+-------------+
| id | select_type | table | type  | possible_keys                                         | key     | key_len | ref  | rows   | Extra       |
+----+-------------+-------+-------+-------------------------------------------------------+---------+---------+------+--------+-------------+
|  1 | SIMPLE      | Job   | range | PRIMARY,Job_lastModified_idx,Job_creationDateTime_idx | PRIMARY | 8       | NULL | 204581 | Using where |
+----+-------------+-------+-------+-------------------------------------------------------+---------+---------+------+--------+-------------+

（注意：此表有426579行，因此不确定204581的来源）

我原以为这会同样快一点？

为什么MySQL在以这种方式编写时无法使用这些索引？

创建一些额外的复合材料索引lastModified＆amp; creationDateTime根本没有帮助。

 create index test_idx1 on Job (lastModified,creationDateTime);
 create index test_idx2 on Job (jobId,lastModified,creationDateTime);

我一定错过了一些简单的事情？

Mysql索引正在考虑但仍有大型表扫描

1 个答案: