系统变量有当前会话(session)变量和全局变量, 它们都以 @@ 开头. 仅以单个@开头的变量为用户变量.

列出所有变量

mysql> show variables;

注意会列出很多.

可以使用LIKE模糊查询变量

SHOW VARIABLES LIKE "%ver%"; 

@@version  存储MySQL的版本

mysql> SELECT @@version;
+-----------+
| @@version |
+-----------+
| 5.5.27    |
+-----------+
1 row in set (0.00 sec)

@@tx_isolation  当前会话的事务隔离级别

mysql> SELECT @@tx_isolation\G;
*************************** 1. row ***************************
@@tx_isolation: REPEATABLE-READ
1 row in set (0.00 sec)

@@global.tx_isolation  当前会话的事务隔离级别

mysql> SELECT @@global.tx_isolation;
+-----------------------+
| @@global.tx_isolation |
+-----------------------+
| REPEATABLE-READ       |
+-----------------------+
1 row in set (0.00 sec)

mysql> SHOW VARIABLES LIKE "innodb_locks_%";
+--------------------------------+-------+
| Variable_name                  | Value |
+--------------------------------+-------+
| innodb_locks_unsafe_for_binlog | OFF   |
+--------------------------------+-------+
1 row in set (0.00 sec)