MySQL 5.7 下的 hint

Posted 2020-12-16 雪胖胖？

参考 https://dev.mysql.com/doc/refman/5.7/en/optimizer-hints.html

Hint Name	Description	Applicable Scopes
BKA, NO_BKA	Affects Batched Key Access join processing	Query block, table
BNL, NO_BNL	Affects Block Nested-Loop join processing	Query block, table
MAX_EXECUTION_TIME	Limits statement execution time	Global
MRR, NO_MRR	Affects Multi-Range Read optimization	Table, index
NO_ICP	Affects Index Condition Pushdown optimization	Table, index
NO_RANGE_OPTIMIZATION	Affects range optimization	Table, index
QB_NAME	Assigns name to query block	Query block
SEMIJOIN, NO_SEMIJOIN	Affects semijoin strategies	Query block
SUBQUERY	Affects materialization, IN-to-EXISTS subquery stratgies	Query block

表级hint，

• BKA, NO_BKA: Enable or disable BKA for the specified tables.
• BNL, NO_BNL: Enable or disable BNL for the specified tables.

索引级别的hint

• MRR, NO_MRR: Enable or disable MRR for the specified table or indexes. MRR hints apply only to InnoDB and MyISAM tables.
• NO_ICP: Disable ICP for the specified table or indexes. By default, ICP is a candidate optimization strategy, so there is no hint for enabling it.
• NO_RANGE_OPTIMIZATION: Disable index range access for the specified table or indexes. This hint also disables Index Merge and Loose Index Scan for the table or indexes. By default, range access is a candidate optimization strategy, so there is no hint for enabling it.

子查询的hint

• SEMIJOIN, NO_SEMIJOIN: Enable or disable the named semijoin strategies.

控制SQL执行时间的hint

• MAX_EXECUTION_TIME(N)

还有个QB_NAME(name)没搞明白。。。

测试了下，好像故意写错了，也没什么影响

mysql> explain select /*+ BNA(fuck_wisedu)*/ a.clusterid,a.ip,a.bak_date,a.start_time,a.end_time,state  from mysql_backup_job a  left join mysql_conf b on a.ip=b.ip  where bak_date = ‘2020-07-08‘  and b.group_id=‘23333‘    and  state = ‘OK‘ ;
+----+-------------+-------+------------+------+-------------------------------------------------------+-------------------------------+---------+----------------+-------+----------+------------------------------------+
| id | select_type | table | partitions | type | possible_keys                                         | key                           | key_len | ref            | rows  | filtered | Extra                              |
+----+-------------+-------+------------+------+-------------------------------------------------------+-------------------------------+---------+----------------+-------+----------+------------------------------------+
|  1 | SIMPLE      | a     | NULL       | ref  | ip_idx,date_idx                                       | date_idx                      | 3       | const          | 15574 |    10.00 | Using where                        |
|  1 | SIMPLE      | b     | NULL       | ref  | IDX_IP                                                | IDX_IP                        | 47      | mysql_bak.a.ip |     1 |    10.00 | Using index condition; Using where |
+----+-------------+-------+------------+------+-------------------------------------------------------+-------------------------------+---------+----------------+-------+----------+------------------------------------+
2 rows in set, 1 warning (0.00 sec)