标签：NO Affects 5.7 hint MRR MySQL table block
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)
标签：NO,Affects,5.7,hint,MRR,MySQL,table,block 来源： https://www.cnblogs.com/Coye/p/13269666.html
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