MySql 8 中的 SQL 查询比 MySql 5.6 慢得多答案

【问题标题】：SQL query much slower in MySql 8 than in MySql 5.6MySql 8 中的 SQL 查询比 MySql 5.6 慢得多
【发布时间】：2021-11-13 17:29:32
【问题描述】：

我有一个简单的查询：

select  count(*)
    from  ror
    where  rorsts not in ( 'RECD', 'CANC', 'CCNS', 'SDNY' )
      and  ( ( rorbcd = '00009310022487'
                      and  rorfid = 'VDR' )
              or  ( rorfid = 'VDR'
                      and  rorbcd in (
                        SELECT  pplbcd
                            from  ppl
                            where  pplfid = 'VDR'
                              and  pplscb6 = '00009310022487'
                              and  pplsflg = 'Y'
                              and  pplsku = '0332690-008'
                              and  ppldoc = '73'
                              and  pplsca9 = ''
                              and  pplven = '10112' ) ) 
           )

在 MySql 5.6 机器上，它运行得非常快：

+----------+
| count(*) |
+----------+
|        2 |
+----------+
1 row in set (0.01 sec)

但在我的 MySql 8 服务器上，它的运行速度要慢得多：

+----------+
| count(*) |
+----------+
|        2 |
+----------+
1 row in set (0.90 sec)

我主要使用两个服务器的默认参数（嗯，Amazon RDS 默认值）。什么参数会导致这种减速？什么配置可以帮助它在 MySql 8 中以与 MySql 5.6 大致相同的速度运行。

根据网上许多其他地方，这是一个糟糕的 SQL。我相信我可以很容易地将它重写为exists，这应该会更有效率。我的问题是我们正在从 5.6 迁移到 8.0，很有可能我会错过一个查询，或者由于我的一些奇怪的要求而无法修复其中一个查询。我敢打赌，我可以在 MySql 8 配置中调整一些参数，以使其以与 5.6 大致相当的方式运行。这就是我要找的。p>

更多信息：

在硬件方面相同的 Amazon RDS 服务器设置
我们刚刚将 5.6 升级到 5.7，然后将 5.7 升级到 8.0。我尽可能使用默认的 MySql 参数。我只是故意更改了lower_case_table_names = 1 和max_connections=300，以匹配 5.6 和我们当前的要求。
PPL 和 ROR 表非常复杂。 PPL 137 列，ROR 144 列。

对于 MySql 5.6 的解释，更简单（而且更快）的查询，以及一些索引信息：

mysql> select version();
+------------+
| version()  |
+------------+
| 5.6.51-log |
+------------+
1 row in set (0.01 sec)

mysql> explain extended select count(*) from ror where rorsts not in ( 'RECD', 'CANC', 'CCNS', 'SDNY' )  and  ( ( rorbcd = '00009310022487' and rorfid = 'VDR'  ) or ( rorfid = 'VDR' and rorbcd in ( select pplbcd from ppl where pplfid = 'VDR' and pplscb6 = '00009310022487' and pplsflg = 'Y' and pplsku = '0332690-008' and ppldoc = '73' and pplsca9 = '' and pplven = '10112'  ) ) );
+----+--------------------+-------+-----------------+----------------------------------------------------------------+--------------+---------+------------+------+----------+------------------------------------+
| id | select_type        | table | type            | possible_keys                                                  | key          | key_len | ref        | rows | filtered | Extra                              |
+----+--------------------+-------+-----------------+----------------------------------------------------------------+--------------+---------+------------+------+----------+------------------------------------+
|  1 | PRIMARY            | ror   | ref             | ROR_RORBCDK,ROR_RORSTSK,ROR_RORBSTSK,ROR_RORSDT3K,ROR_RORGMOQK | ROR_RORGMOQK | 5       | const      |    1 |   100.00 | Using index condition; Using where |
|  2 | DEPENDENT SUBQUERY | ppl   | unique_subquery | PPL_PPLBCDC,PPL_PPLDOCK,PPL_PPLVENC,PPL_PPLSKUC,PPL_PPLFID     | PPL_PPLBCDC  | 29      | func,const |    1 |   100.00 | Using where                        |
+----+--------------------+-------+-----------------+----------------------------------------------------------------+--------------+---------+------------+------+----------+------------------------------------+
2 rows in set, 1 warning (0.00 sec)

mysql> show warnings;                                                                                                                                                                                                                         +-------+------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Level | Code | Message                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
+-------+------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Note  | 1003 | /* select#1 */ select count(0) AS `count(*)` from `celltreat`.`ror` where ((`celltreat`.`ror`.`RORSTS` not in ('RECD','CANC','CCNS','SDNY')) and (((`celltreat`.`ror`.`RORFID` = 'VDR') and (`celltreat`.`ror`.`RORBCD` = '00009310022487')) or ((`celltreat`.`ror`.`RORFID` = 'VDR') and <in_optimizer>(`celltreat`.`ror`.`RORBCD`,<exists>(<primary_index_lookup>(<cache>(`celltreat`.`ror`.`RORBCD`) in ppl on PPL_PPLBCDC where ((`celltreat`.`ppl`.`PPLVEN` = '10112') and (`celltreat`.`ppl`.`PPLSCA9` = '') and (`celltreat`.`ppl`.`PPLDOC` = '73') and (`celltreat`.`ppl`.`PPLSKU` = '0332690-008') and (`celltreat`.`ppl`.`PPLSFLG` = 'Y') and (`celltreat`.`ppl`.`PPLSCB6` = '00009310022487') and (`celltreat`.`ppl`.`PPLFID` = 'VDR') and (<cache>(`celltreat`.`ror`.`RORBCD`) = `celltreat`.`ppl`.`PPLBCD`)))))))) |
+-------+------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> 
mysql> select count(*) from ppl;
+----------+
| count(*) |
+----------+
|    95108 |
+----------+
1 row in set (0.01 sec)

mysql> explain extended select count(*) from ppl;
+----+-------------+-------+-------+---------------+------------+---------+------+-------+----------+-------------+
| id | select_type | table | type  | possible_keys | key        | key_len | ref  | rows  | filtered | Extra       |
+----+-------------+-------+-------+---------------+------------+---------+------+-------+----------+-------------+
|  1 | SIMPLE      | ppl   | index | NULL          | PPL_PPLFID | 5       | NULL | 11194 |   100.00 | Using index |
+----+-------------+-------+-------+---------------+------------+---------+------+-------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

mysql> show warnings;
+-------+------+---------------------------------------------------------------------+
| Level | Code | Message                                                             |
+-------+------+---------------------------------------------------------------------+
| Note  | 1003 | /* select#1 */ select count(0) AS `count(*)` from `celltreat`.`ppl` |
+-------+------+---------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql>
mysql> SELECT TABLE_NAME,  index_name, COUNT(1) column_count FROM INFORMATION_SCHEMA.STATISTICS WHERE TABLE_SCHEMA = 'veeder' and table_name in ( 'ppl', 'ror' ) group by table_name, index_name order by table_name collate utf8_general_ci, index_name collate utf8_general_ci;
+------------+--------------+--------------+
| TABLE_NAME | index_name   | column_count |
+------------+--------------+--------------+
| ppl        | PPLKEY       |            1 |
| ppl        | PPL_PPLBCDC  |            2 |
| ppl        | PPL_PPLDOCK  |            3 |
| ppl        | PPL_PPLFID   |            1 |
| ppl        | PPL_PPLPONOC |            4 |
| ppl        | PPL_PPLSKUC  |            4 |
| ppl        | PPL_PPLVENC  |            5 |
| ror        | RORKEY       |            1 |
| ror        | ROR_RORBCDK  |            5 |
| ror        | ROR_RORBSTSK |            4 |
| ror        | ROR_RORCNSK  |            3 |
| ror        | ROR_RORCRDTK |            4 |
| ror        | ROR_RORCUIDK |            5 |
| ror        | ROR_RORDOCK  |            5 |
| ror        | ROR_RORGMOQK |            4 |
| ror        | ROR_RORPONOK |            6 |
| ror        | ROR_RORRORK  |            2 |
| ror        | ROR_RORSDT3K |            4 |
| ror        | ROR_RORSKUK  |            5 |
| ror        | ROR_RORSTSK  |            5 |
| ror        | ROR_RORUSTSK |            4 |
| ror        | ROR_RORVENK  |            7 |
| ror        | ROR_RORVSTSK |            4 |
+------------+--------------+--------------+
23 rows in set (0.00 sec)

现在是 MySQL 8 的解释，带有更简单（但更慢）的查询，以及一些索引信息：

mysql> select version();
+-----------+
| version() |
+-----------+
| 8.0.23    |
+-----------+
1 row in set (0.00 sec)

mysql> explain select count(*) from ror where rorsts not in ( 'RECD', 'CANC', 'CCNS', 'SDNY' )  and  ( ( rorbcd = '00009310022487' and rorfid = 'VDR'  ) or ( rorfid = 'VDR' and rorbcd in ( select pplbcd from ppl where pplfid = 'VDR' and pplscb6 = '00009310022487' and pplsflg = 'Y' and pplsku = '0332690-008' and ppldoc = '73' and pplsca9 = '' and pplven = '10112'  ) ) );
+----+-------------+-------+------------+------+----------------------------------------------------------------+--------------+---------+-------------------------+--------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys                                                  | key          | key_len | ref                     | rows   | filtered | Extra       |
+----+-------------+-------+------------+------+----------------------------------------------------------------+--------------+---------+-------------------------+--------+----------+-------------+
|  1 | PRIMARY     | ror   | NULL       | ref  | ROR_RORBCDK,ROR_RORSTSK,ROR_RORBSTSK,ROR_RORSDT3K,ROR_RORGMOQK | ROR_RORGMOQK | 5       | const                   | 185179 |    50.03 | Using where |
|  2 | SUBQUERY    | ppl   | NULL       | ref  | PPL_PPLBCDC,PPL_PPLDOCK,PPL_PPLVENC,PPL_PPLSKUC,PPL_PPLFID     | PPL_PPLVENC  | 53      | const,const,const,const |      2 |     2.50 | Using where |
+----+-------------+-------+------------+------+----------------------------------------------------------------+--------------+---------+-------------------------+--------+----------+-------------+
2 rows in set, 1 warning (0.02 sec)

mysql> show warnings;
+-------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Level | Code | Message                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
+-------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Note  | 1003 | /* select#1 */ select count(0) AS `count(*)` from `veeder`.`ror` where ((`veeder`.`ror`.`RORSTS` not in ('RECD','CANC','CCNS','SDNY')) and (((`veeder`.`ror`.`RORFID` = 'VDR') and (`veeder`.`ror`.`RORBCD` = '00009310022487')) or ((`veeder`.`ror`.`RORFID` = 'VDR') and <in_optimizer>(`veeder`.`ror`.`RORBCD`,`veeder`.`ror`.`RORBCD` in ( <materialize> (/* select#2 */ select `veeder`.`ppl`.`PPLBCD` from `veeder`.`ppl` where ((`veeder`.`ppl`.`PPLVEN` = '10112') and (`veeder`.`ppl`.`PPLSCA9` = '') and (`veeder`.`ppl`.`PPLDOC` = '73') and (`veeder`.`ppl`.`PPLSKU` = '0332690-008') and (`veeder`.`ppl`.`PPLSFLG` = 'Y') and (`veeder`.`ppl`.`PPLSCB6` = '00009310022487') and (`veeder`.`ppl`.`PPLFID` = 'VDR')) ), <primary_index_lookup>(`veeder`.`ror`.`RORBCD` in <temporary table> on <auto_distinct_key> where ((`veeder`.`ror`.`RORBCD` = `<materialized_subquery>`.`pplbcd`)))))))) |
+-------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> 
mysql> select count(*) from ppl;
+----------+
| count(*) |
+----------+
|    94657 |
+----------+
1 row in set (0.49 sec)

mysql> explain select count(*) from ppl;
+----+-------------+-------+------------+-------+---------------+------------+---------+------+-------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key        | key_len | ref  | rows  | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+------------+---------+------+-------+----------+-------------+
|  1 | SIMPLE      | ppl   | NULL       | index | NULL          | PPL_PPLFID | 5       | NULL | 89284 |   100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+------------+---------+------+-------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

mysql> show warnings;
+-------+------+------------------------------------------------------------------+
| Level | Code | Message                                                          |
+-------+------+------------------------------------------------------------------+
| Note  | 1003 | /* select#1 */ select count(0) AS `count(*)` from `veeder`.`ppl` |
+-------+------+------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> SELECT TABLE_NAME,  index_name, COUNT(1) column_count FROM INFORMATION_SCHEMA.STATISTICS WHERE TABLE_SCHEMA = 'veeder' and table_name in ( 'ppl', 'ror' ) group by table_name, index_name order by table_name collate utf8_general_ci, index_name collate utf8_general_ci;
+------------+--------------+--------------+
| TABLE_NAME | INDEX_NAME   | column_count |
+------------+--------------+--------------+
| ppl        | PPLKEY       |            1 |
| ppl        | PPL_PPLBCDC  |            2 |
| ppl        | PPL_PPLDOCK  |            3 |
| ppl        | PPL_PPLFID   |            1 |
| ppl        | PPL_PPLPONOC |            4 |
| ppl        | PPL_PPLSKUC  |            4 |
| ppl        | PPL_PPLVENC  |            5 |
| ror        | RORKEY       |            1 |
| ror        | ROR_RORBCDK  |            5 |
| ror        | ROR_RORBSTSK |            4 |
| ror        | ROR_RORCNSK  |            3 |
| ror        | ROR_RORCRDTK |            4 |
| ror        | ROR_RORCUIDK |            5 |
| ror        | ROR_RORDOCK  |            5 |
| ror        | ROR_RORGMOQK |            4 |
| ror        | ROR_RORPONOK |            6 |
| ror        | ROR_RORRORK  |            2 |
| ror        | ROR_RORSDT3K |            4 |
| ror        | ROR_RORSKUK  |            5 |
| ror        | ROR_RORSTSK  |            5 |
| ror        | ROR_RORUSTSK |            4 |
| ror        | ROR_RORVENK  |            7 |
| ror        | ROR_RORVSTSK |            4 |
+------------+--------------+--------------+
23 rows in set (0.01 sec)

我不明白 MySql 8 给出的警告，但也许这是找到正确服务器设置的关键。

表定义和索引有点长，特别是对于两个数据库，但我确实有它们的副本，它们看起来几乎相同。最大的区别似乎是在 5.6 中我将一些整数列定义为“int(11)”，而在 8.0 中，它们被定义为“int”。在“show create table”输出中，索引是相同的。显然，“AUTO_INCREMENT”值是不同的，但这是有道理的，因为 MySql 8 版本已经过时了一周。希望这是足够的信息。当我在两个数据库服务器上执行“describe ppl”、“show index from ppl”、“describe ror”和“show index from ror”时，它们实际上是相同的，除了以下几点：

如上，int(11) 改为int。
“基数”列发生变化。 MySQL 8 版本较少，可能是因为它已经过时了
显然，8.0“显示索引”命令显示更多列。 “可见”列始终为“YES”，“表达式”列始终为“NULL”。顺便说一下，INDEX_TYPE 对于所有索引都是“BTREE”。

因为这些表格有点大，show create table 和 describe <table>;show indexes from <table> 产生的结果对于帖子的正文来说太长了。因此，如果您需要更多信息，我需要知道您不需要我目前提供的内容。谢谢。

编辑：

在应用@o-jones 的建议后进行编辑： 下面的结果是我运行ANALYZE TABLE ror, ppl; 之后的结果，但它们与我运行ANALYZE TABLE ror, ppl; 之前发生的情况相匹配。

mysql> select version();
+-----------+
| version() |
+-----------+
| 8.0.23    |
+-----------+
1 row in set (0.00 sec)

mysql> explain select count(*) from ror where rorsts not in ( 'RECD', 'CANC', 'CCNS', 'SDNY' )  and  ( ( rorbcd = '00009310022487' and rorfid = 'VDR'  ) or ( rorfid = 'VDR' and rorbcd in ( select pplbcd from ppl where pplfid = 'VDR' and '00009310022487' and pplsflg = 'Y' and pplsku = '0332690-008' and ppldoc = '73' and pplsca9 = '' and pplven = '10112'  ) ) );
+----+-------------+-------+------------+------+----------------------------------------------------------------+--------------+---------+-------------------------+--------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys                                                  | key          | key_len | ref                     | rows   | filtered | Extra       |
+----+-------------+-------+------------+------+----------------------------------------------------------------+--------------+---------+-------------------------+--------+----------+-------------+
|  1 | PRIMARY     | ror   | NULL       | ref  | ROR_RORBCDK,ROR_RORSTSK,ROR_RORBSTSK,ROR_RORSDT3K,ROR_RORGMOQK | ROR_RORGMOQK | 5       | const                   | 185179 |    50.03 | Using where |
|  2 | SUBQUERY    | ppl   | NULL       | ref  | PPL_PPLBCDC,PPL_PPLDOCK,PPL_PPLVENC,PPL_PPLSKUC,PPL_PPLFID     | PPL_PPLVENC  | 53      | const,const,const,const |      2 |     2.50 | Using where |
+----+-------------+-------+------------+------+----------------------------------------------------------------+--------------+---------+-------------------------+--------+----------+-------------+
2 rows in set, 1 warning (0.01 sec)

mysql> select count(*) from ror where rorsts not in ( 'RECD', 'CANC', 'CCNS', 'SDNY' )  and  ( ( rorbcd = '00009310022487' and rorfid = 'VDR'  ) or ( rorfid = 'VDR' and rorbcd in ( select pplbcd from ppl where pplfid = 'VDR' and pplscb610022487' and pplsflg = 'Y' and pplsku = '0332690-008' and ppldoc = '73' and pplsca9 = '' and pplven = '10112'  ) ) );
+----------+
| count(*) |
+----------+
|        2 |
+----------+
1 row in set (0.80 sec)

mysql> explain select count(*) from ror USE INDEX(ROR_RORSTSK) where rorsts not in ( 'RECD', 'CANC', 'CCNS', 'SDNY' )  and  ( ( rorbcd = '00009310022487' and rorfid = 'VDR'  ) or ( rorfid = 'VDR' and rorbcd in ( select pplbcd from ppl wd = 'VDR' and pplscb6 = '00009310022487' and pplsflg = 'Y' and pplsku = '0332690-008' and ppldoc = '73' and pplsca9 = '' and pplven = '10112'  ) ) );
+----+-------------+-------+------------+------+------------------------------------------------------------+-------------+---------+-------------------------+--------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys                                              | key         | key_len | ref                     | rows   | filtered | Extra       |
+----+-------------+-------+------------+------+------------------------------------------------------------+-------------+---------+-------------------------+--------+----------+-------------+
|  1 | PRIMARY     | ror   | NULL       | ALL  | ROR_RORSTSK                                                | NULL        | NULL    | NULL                    | 370358 |    50.03 | Using where |
|  2 | SUBQUERY    | ppl   | NULL       | ref  | PPL_PPLBCDC,PPL_PPLDOCK,PPL_PPLVENC,PPL_PPLSKUC,PPL_PPLFID | PPL_PPLVENC | 53      | const,const,const,const |      2 |     2.50 | Using where |
+----+-------------+-------+------------+------+------------------------------------------------------------+-------------+---------+-------------------------+--------+----------+-------------+
2 rows in set, 1 warning (0.00 sec)

mysql> select count(*) from ror USE INDEX(ROR_RORSTSK) where rorsts not in ( 'RECD', 'CANC', 'CCNS', 'SDNY' )  and  ( ( rorbcd = '00009310022487' and rorfid = 'VDR'  ) or ( rorfid = 'VDR' and rorbcd in ( select pplbcd from ppl where ppl' and pplscb6 = '00009310022487' and pplsflg = 'Y' and pplsku = '0332690-008' and ppldoc = '73' and pplsca9 = '' and pplven = '10112'  ) ) );
+----------+
| count(*) |
+----------+
|        2 |
+----------+
1 row in set (0.25 sec)

mysql> explain select count(*) from ror where rorsts not in ( 'RECD', 'CANC', 'CCNS', 'SDNY' )  and  ( ( rorbcd = '00009310022487' and rorfid = 'VDR'  ) );+----+-------------+-------+------------+-------+----------------------------------------------------------------+--------------+---------+------+------+----------+--------------------------+
| id | select_type | table | partitions | type  | possible_keys                                                  | key          | key_len | ref  | rows | filtered | Extra                    |
+----+-------------+-------+------------+-------+----------------------------------------------------------------+--------------+---------+------+------+----------+--------------------------+
|  1 | SIMPLE      | ror   | NULL       | range | ROR_RORBCDK,ROR_RORSTSK,ROR_RORBSTSK,ROR_RORSDT3K,ROR_RORGMOQK | ROR_RORBSTSK | 35      | NULL |   37 |   100.00 | Using where; Using index |
+----+-------------+-------+------------+-------+----------------------------------------------------------------+--------------+---------+------+------+----------+--------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> select count(*) from ror where rorsts not in ( 'RECD', 'CANC', 'CCNS', 'SDNY' )  and  ( ( rorbcd = '00009310022487' and rorfid = 'VDR'  ) );
+----------+
| count(*) |
+----------+
|        2 |
+----------+
1 row in set (0.00 sec)

顺便说一句，在这种情况下，使用索引提示不是一个可接受的解决方案，因为这只是一个示例 SQL。我一直都知道我可以让这个特定的 SQL 更高效。我的问题是，对于相同的 SQL，MySql 8 应该更快，但速度要慢得多，因此试图找出原因。我怀疑在 MySql 5.7 中也会发生同样的事情，但我还没有尝试过，因为我听说 MySql 8 是要走的路。

【问题讨论】：

请read this 然后edit 提供更多信息，包括您的表定义和两个版本的MySql 中EXPLAIN 的输出。
我只是在问为什么完全相同的 SQL 工作方式不同。我知道我可以通过多种方式改进这个特定的 SQL。有没有影响这一点的配置？
而且我们不能告诉你为什么相同的 sql 语句在两个 mysql 版本中运行不同，而没有看到你的数据结构和两个版本中的解释输出。相信我，mysql v8 中没有神奇的设置会突然导致查询运行速度变慢或变快！
v8 查询计划器与 v5.6 中的查询计划器完全不同。此外，您可能已经更改了存储引擎，甚至可能您的索引已更改。如果您的问题的答案是“将 framis 变量设置为 42”，那就太好了，但事情并不是那么简单，很遗憾。
请为每张桌子提供SHOW CREATE TABLE。每个版本都有EXPLAIN SELECT ...。

标签： mysql query-optimization amazon-rds mysql-8.0 mysql-5.6

【解决方案1】：

主要（顶级）查询的查询计划——使用您的ror 表的查询计划——比较。

version  type   key        key_len  ref     rows Filtered Extra
 5.6.61 range  ROR_RORSTSK       6  NULL    3256    ----  Using index condition; Using where 
 8.0.23 ref    ROR_RORGMOQK      5  const 185179    50.03 Using where

由于某种原因，8.0.23 查询优化器没有选择 ROR_RORSTSK 索引来满足您的查询，而是选择了 ROR_RORGMOQK。结果，查询不能使用范围扫描，必须过滤（逐一比较）185k 行而不是 3k 行。这就是您的两个计划之间的明显区别。

（5.6 EXPLAIN 输出不包括 Filtered 列。您需要 EXPLAIN EXTENDED。）

您可以尝试在查询中更改此行

from ror

到

from ror USE INDEX(ROR_RORSTSK)

或

from ror IGNORE INDEX(ROR_RORGMOQK)

其中一个可能会让 v8 使用与 v5.6 类似的查询计划。

根据您对每个索引中包含哪些列的了解，您可能可以了解更多信息。

编辑

还可以尝试执行ANALYZE TABLE ror, ppl;，尤其是如果您只是在迁移过程中批量加载表。如果ANALYZE 是不必要的，它不会伤害任何东西，它可以帮助查询规划器选择最佳计划。

【讨论】：

所以基本上，由于某种原因，MySql 8 没有选择正确的索引。我什至没有注意到它正在找到一个完全不同的索引，这很奇怪。我会做实验。
仅供参考：实际上，我后来发现如果我将explain 更改为explain extended，它将为我提供 MySql 5.6 的过滤列。我只是懒得相应地更新我的原始帖子。
ANALYZE 什么也没做。我认为这发生在升级过程中，但是，就像你说的，尝试没有坏处。根据explain，它仍然选择了错误的索引。我将使用此信息更新主帖，并深入研究ANALYZE 以确保我没有错过一些特殊选项。