MySQL sql_mode修改不生效的原因及解决

近期多次聊到sql_mode的话题，也是多次遇到相关问题，今天就趁热打铁，再给大家带来一个sql_mode的案例分享。

基于业务敏感性的考虑，下面涉及的表、存储过程等均非真实数据，但并不影响排查过程。

（1）客户侧开发童鞋创建了一个存储过程，该存储过程没有严格遵守group by标准语法

session 1：mysql> delimiter //mysql> create procedure test_for_group_by() -> begin -> select k,pad,count(*) from test.test group by k; -> end //Query OK, 0 rows affected (0.01 sec)mysql> delimiter ;

（2）客户侧开发童鞋调用该存储过程，报错ERROR 1140；因为当时存储过程比较复杂，改造起来比较麻烦，所以客户侧选择修改sql_mode

session 1：mysql> call test_for_group_by();ERROR 1140 (42000): In aggregated query without GROUP BY, expression #1 of SELECT list contains nonaggregated column ’test.test.k’; this is incompatible with sql_mode=only_full_group_by

（3）客户侧修改完sql_mode，再次执行，发现仍然报错ERROR 1140

session 2：mysql> set global sql_mode=’STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION’;Query OK, 0 rows affected (0.00 sec)session 1：mysql> call test_for_group_by();ERROR 1140 (42000): In aggregated query without GROUP BY, expression #1 of SELECT list contains nonaggregated column ’test.test.k’; this is incompatible with sql_mode=only_full_group_by

（4）此时想到，修改系统变量，只对新建连接有效，对已有连接不起作用；于是，让客户侧重新建立连接，确认系统变量已生效，再次调用存储过程，但仍然报错ERROR 1140，重复尝试几次都是这个结果

session 3：mysql> show variables like ’sql_mode’;+---------------+------------------------------------------------------------------------------------------------------------------------+| Variable_name | Value |+---------------+------------------------------------------------------------------------------------------------------------------------+| sql_mode | STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |+---------------+------------------------------------------------------------------------------------------------------------------------+1 row in set (0.01 sec)mysql> call test_for_group_by();ERROR 1140 (42000): In aggregated query without GROUP BY, expression #1 of SELECT list contains nonaggregated column ’test.test.k’; this is incompatible with sql_mode=only_full_group_by

（5）进一步排查，让客户侧在该会话，执行非标准的group by语句，发现可以正常执行

session 3：mysql> select user,host,count(*) From mysql.user group by user;+---------------+-----------+----------+| user | host | count(*) |+---------------+-----------+----------+| mysql.session | localhost |1 || mysql.sys | localhost |1 || root | localhost |1 || rpl_user | % |1 || test | % |1 |+---------------+-----------+----------+5 rows in set (0.00 sec)

（6）继续排查发现，该存储过程的sql_mode，还是包括ONLY_FULL_GROUP_BY，因此执行报错

session 2：mysql> select routine_catalog,routine_schema,routine_name,routine_type,created,last_altered,sql_mode from routines where routine_name=’test_for_group_by’;+-----------------+----------------+-------------------+--------------+---------------------+---------------------+-------------------------------------------------------------------------------------------------------------------------------------------+| routine_catalog | routine_schema | routine_name | routine_type | created | last_altered| sql_mode |+-----------------+----------------+-------------------+--------------+---------------------+---------------------+-------------------------------------------------------------------------------------------------------------------------------------------+| def | test | test_for_group_by | PROCEDURE | 2020-12-24 12:12:10 | 2020-12-24 12:12:10 | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |+-----------------+----------------+-------------------+--------------+---------------------+---------------------+-------------------------------------------------------------------------------------------------------------------------------------------+1 row in set (0.00 sec)

（7）这里我们也可以知道，系统变量修改只对新建对象有效，对已有对象不生效；解决办法很简单，重建该存储过程即可

session 3：mysql> drop procedure test_for_group_by;Query OK, 0 rows affected (0.01 sec)mysql> delimiter //mysql> create procedure test_for_group_by() -> begin -> select k,pad,count(*) from test.test group by k; -> end //Query OK, 0 rows affected (0.01 sec)mysql> delimiter ;mysql> call test_for_group_by();+--------+-------------------------------------------------------------+----------+| k | pad | count(*) |+--------+-------------------------------------------------------------+----------+| 393975 | 35227182905-15234265621-59793845249-15413569710-23749555118 |1 || 495688 | 09512147864-77936258834-40901700703-13541171421-15205431759 |1 || 497896 | 13152283289-69561545685-52868757241-04245213425-69280254356 |1 || 498573 | 43131080328-59298106536-35954612339-97546855884-75769514803 |1 || 500775 | 27590239742-20204899609-34345212327-79811525340-24267764271 |1 || 501885 | 63188288836-92351140030-06390587585-66802097351-49282961843 |1 || 503330 | 01495266405-82925129145-92643983850-90243995398-18709399387 |1 || 503666 | 40929980986-33813039690-13155419391-97985458477-39771362212 |1 || 504353 | 00505722282-72931248925-57037623248-81117963809-88658076981 |1 || 514246 | 21979564480-87492594656-60524686334-78820761788-57684966682 |1 |+--------+-------------------------------------------------------------+----------+10 rows in set (0.00 sec)Query OK, 0 rows affected (0.00 sec)总结

通过这个案例，我们可以知道，修改sql_mode系统变量，只对新建连接和新建对象(主要包括函数和存储过程)有效，对已有连接和已有对象不生效。

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