SET [GLOBAL|SESSION] <variable>
注意
与 MySQL 类似,对 GLOBAL
变量的更改不适用于已有连接或本地连接,只有新会话才会反映值的变化。
VariableAssignment:
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
| Variable_name | Value |
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
| sql_mode | 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)
SHOW SESSION VARIABLES LIKE 'sql_mode';
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
| Variable_name | Value |
| sql_mode | 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)
更新全局的 sql_mode
:
Query OK, 0 rows affected (0.03 sec)
检查更新之后的 sql_mode
的取值,可以看到 SESSION 级别的值没有更新:
SHOW GLOBAL VARIABLES LIKE 'sql_mode';
+---------------+-----------------------------------------+
| Variable_name | Value |
+---------------+-----------------------------------------+
| sql_mode | STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER |
+---------------+-----------------------------------------+
1 row in set (0.00 sec)
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
| Variable_name | Value |
| sql_mode | 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)
SET SESSION
则可以立即生效:
SET SESSION sql_mode = 'STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER';
Query OK, 0 rows affected (0.01 sec)
+---------------+-----------------------------------------+
| Variable_name | Value |
+---------------+-----------------------------------------+
| sql_mode | STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER |
+---------------+-----------------------------------------+
1 row in set (0.00 sec)
- 与 MySQL 不同,TiDB 中使用
SET GLOBAL
所作的修改会应用于集群中的全部 TiDB 实例。而在 MySQL 中,修改不会应用于副本。 - TiDB 中的若干变量可读又可设置,这是与 MySQL 相兼容的要求,因为应用程序和连接器常读取 MySQL 变量。例如:JDBC 连接器同时读取和设置缓存查询的参数,尽管并不依赖这一行为。