Question

我的简单查询花了太长时间才返回结果。这是我的疑问：

select count(*) from f_logs as a 
where a.id = (
    select max(id) 
    from f_logs 
    where f_id = a.f_id 
    group by f_id
) and log_status = 'In storage';

这是我表格中的样本数据：

+----+-------+------------+------------+-----------------+-------------+----------------+-------------+
| id | f_id  | log_date   | log_action | log_destination | log_remarks | log_status     | log_account |
+----+-------+------------+------------+-----------------+-------------+----------------+-------------+
|  1 | 1-EC  | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
|  2 | 2-EC  | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
|  3 | 3-EC  | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
|  4 | 4-EC  | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
|  5 | 5-EC  | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
|  6 | 1-EC  | 2017-05-03 | Released   | Treasury        |             | Not in Storage | Person A    |
|  7 | 7-EC  | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
|  8 | 8-EC  | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
|  9 | 2-EC  | 2017-05-03 | Released   | Registrar       |             | Not in Storage | Person A    |
| 10 | 10-EC | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
| 11 | 11-EC | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
| 12 | 12-EC | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
| 13 | 3-EC  | 2017-05-03 | Released   | Registrar       |             | Not in Storage | Person B    |
| 14 | 14-EC | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
| 15 | 15-EC | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
| 16 | 16-EC | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
| 17 | 17-EC | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
| 18 | 18-EC | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
| 19 | 19-EC | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
| 20 | 1-EC  | 2017-05-03 | Receive    | Records Unit    |             | In storage     | Records     |
+----+-------+------------+------------+-----------------+-------------+----------------+-------------+

使用explain返回以下内容：

+----+--------------------+--------+------------+------+---------------+------+---------+------+-------+----------+----------------------------------------------+
| id | select_type        | table  | partitions | type | possible_keys | key  | key_len | ref  | rows  | filtered | Extra                                        |
+----+--------------------+--------+------------+------+---------------+------+---------+------+-------+----------+----------------------------------------------+
|  1 | PRIMARY            | a      | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 46439 |    10.00 | Using where                                  |
|  2 | DEPENDENT SUBQUERY | f_logs | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 46439 |    10.00 | Using where; Using temporary; Using filesort |
+----+--------------------+--------+------------+------+---------------+------+---------+------+-------+----------+----------------------------------------------+
2 rows in set, 2 warnings (0.00 sec)

Note (Code 1276): Field or reference 'gsis_new.a.f_id' of SELECT #2 was resolved in SELECT #1
Note (Code 1003): 
/* select#1 */
select count(0) AS count(*) 
from gsis_new.f_logs a 
where ((gsis_new.a.id = (

    /* select#2 */ 
    select max(gsis_new.f_logs.id) 
    from gsis_new.f_logs 
    where (gsis_new.f_logs.f_id = gsis_new.a.f_id) 
    group by gsis_new.f_logs.f_id)

) and (gsis_new.a.log_status = 'In storage'))

这就是我想要发生的事情：我有一个名为f_logs的表，它用于记录文件。我想返回表中记录的总数。

从我的样本表数据。它应该返回＆＃39; 14＆＃39;因为2-EC和3-EC被标记为不存储在第9行和第13行中虽然1-EC已经在第20行再次标记为存储。

注意：当未填充表时，我的mySql查询工作正常。
有没有机会优化我的查询？

附加信息：这是我的f_logs表的索引

+--------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table  | Non_unique | Key_name    | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| f_logs |          0 | PRIMARY     |            1 | id          | A         |       46439 |     NULL | NULL   |      | BTREE      |         |               |
| f_logs |          1 | acountIndex |            1 | log_account | A         |           1 |     NULL | NULL   | YES  | BTREE      |         |               |
+--------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

Answer 1

您的解释显示表格中可能没有索引。

ALTER TABLE f_logs ADD INDEX (id), ADD INDEX (f_id);

MySQL简单查询花了很长时间才返回结果

1 个答案: