我调试了一个花了太多时间的MYSQL查询。
查询是这样的：
WHERE 1=1
GROUP BY TM.tutor_id
ORDER BY TM.is_priority DESC, TM.tutor_id DESC LIMIT 0, 10
如果我要排除部分
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE TM ALL NULL NULL NULL NULL 27530 Using temporary; Using filesort
1 SIMPLE CM eq_ref PRIMARY PRIMARY 4 toprecru_portal_db.TM.category 1
1 SIMPLE TER ALL NULL NULL NULL NULL 13223
1 SIMPLE SHM ref tutor_id,user_auth_id user_auth_id 257 const 1
1 SIMPLE LM ALL NULL NULL NULL NULL 11
Query执行如下：
显示0到29行（总共27,649行，查询占用0.2339秒）
对于完整查询，它是这样的：
显示0到9行（总计10行，查询耗时115.4066秒）
我为查询中使用的所有字段编制了索引。
MYSQL解释如下：
read_buffer_size = 512M
join_buffer_size = 512M
sort_buffer_size = 256M
更新
我在某处读到使用1 = 1并没有对性能产生影响，但即使添加1 = 1，查询也需要从0.2339秒开始大约70秒。
MYSQL my.cnf设置如下：
id tutor_id level_id exp_rate
1 27597 4 $30-35/hr
2 27597 10 $40-45/hr
99 27598 5 35-40/hr minimum
124 27602 4 25-30/hr or 30-40/hr minimum 1.5hrs per session
125 27602 0
更新
当使用group_by而没有order_by时，时间几乎相同：
显示0到29行（总共27,530行，查询占用114.9642秒）
更新样品日期： 表 - 导师预期费率
admin_shortlist_id job_ad_id request_profile_id tutor_id user_auth_id added_date
143693 0 0 22692 4ef44ea2203114a3e27eaff31a1bf3be 2015-09-17
143694 0 0 11653 4ef44ea2203114a3e27eaff31a1bf3be 2015-09-17
143695 0 0 27611 4ef44ea2203114a3e27eaff31a1bf3be 2015-09-17
143696 0 0 27610 4ef44ea2203114a3e27eaff31a1bf3be 2015-09-17
296793 0 13 0 21232f297a57a5a743894a0e4a801fc3 2015-10-05
表 - admin_shortlist_master
category_id category_name disp_order status 0-Not Published, 1-Published
1 Polytechnic Student 0 1
2 Diploma Grad Part Time 1 1
3 Diploma Grad Full Time 2 1
4 JC Student 3 0
5 A Level Grad Part Time 4 1
table-category master
level_id level_name class_title class_ids subject_ids status 0-Not Published, 1-Published
4 Primary Primary 4,5,6,7,8,9,10 5,6,7,8,9,10,11,12,14,15 1
5 O Level (Secondary) Secondary 12,13,14,15,16
4,5,6,7,8,9,10,13,14,15,16,17,18,19,20,21,22,23,24... 1
6 A Level (JC) JC 18,19,20 6,17,18,19,23,24,25,26,30,31,32,33,34,35,36,37,38,... 1
7 International Baccalaureate 17,18,19,23,24,34,40,41,42,43,44,45,46,47,48,49,50... 1
8 Diploma 26,34,47,54,55,56,57,59,60,61,62,63,64,65,66,67,68... 1
表级主人
select tutor_id, category, is_priority, birthdate from tutor_master order by tutor_id limit 5
tutor_id Ascending 1 category is_priority birthdate
4 8 0 1989-01-01
7 8 0 1987-01-01
8 8 0 1964-01-01
9 2 0 1987-01-01
10 8 0 1983-01-01
更新：
N答案 0 :(得分：0)
如果不知道表格结构并拥有一些示例数据（如果您可以编辑原始问题以包含这些问题并帮助），则很难调试。看来你最大的问题是所有牌桌都没有标记。
你应该能够获得这样的输出，其中一切都在使用索引：
+------+-------------+-------+--------+---------------+----------+---------+--------------------------+------+--------------------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+-------------+-------+--------+---------------+----------+---------+--------------------------+------+--------------------------------------------------------------+
| 1 | SIMPLE | TM | ALL | NULL | NULL | NULL | NULL | 2 | Using temporary; Using filesort |
| 1 | SIMPLE | CM | eq_ref | PRIMARY | PRIMARY | 4 | tutors.TM.category | 1 | Using index |
| 1 | SIMPLE | TER | index | NULL | tutor_id | 8 | NULL | 1 | Using where; Using index; Using join buffer (flat, BNL join) |
| 1 | SIMPLE | SHM | eq_ref | tutor_id | tutor_id | 606 | tutors.TM.tutor_id,const | 1 | Using where; Using index |
| 1 | SIMPLE | LM | index | NULL | PRIMARY | 4 | NULL | 1 | Using where; Using index; Using join buffer (flat, BNL join) |
+------+-------------+-------+--------+---------------+----------+---------+--------------------------+------+--------------------------------------------------------------+
因为您正在使用FIND_IN_SET，您可能无法删除联接缓冲区，而且似乎始终需要对导师进行全表扫描，这不应该是一个问题
这些是我对所有表格的指标：
MariaDB [tutors]> show indexes from admin_shortlist_master;
+------------------------+------------+----------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+------------------------+------------+----------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| admin_shortlist_master | 0 | PRIMARY | 1 | id | A | 0 | NULL | NULL | | BTREE | | |
| admin_shortlist_master | 0 | tutor_id | 1 | tutor_id | A | 0 | NULL | NULL | | BTREE | | |
| admin_shortlist_master | 0 | tutor_id | 2 | user_auth_id | A | 0 | NULL | NULL | | BTREE | | |
+------------------------+------------+----------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.00 sec)
MariaDB [tutors]> show indexes from category_master;
+-----------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-----------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| category_master | 0 | PRIMARY | 1 | category_id | A | 0 | NULL | NULL | | BTREE | | |
+-----------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)
MariaDB [tutors]> show indexes from level_master;
+--------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| level_master | 0 | PRIMARY | 1 | level_id | A | 0 | NULL | NULL | | BTREE | | |
+--------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)
MariaDB [tutors]> show indexes from tutor_expected_rate;
+---------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+---------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| tutor_expected_rate | 0 | PRIMARY | 1 | id | A | 0 | NULL | NULL | | BTREE | | |
| tutor_expected_rate | 0 | tutor_id | 1 | tutor_id | A | 0 | NULL | NULL | | BTREE | | |
| tutor_expected_rate | 0 | tutor_id | 2 | level_id | A | 0 | NULL | NULL | | BTREE | | |
+---------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.00 sec)
如果您想提供整体结构和一些示例数据，那么很可能还有一种方法可以为tutor_master表编制索引，但目前很难确定。