如何在MySQL中的命令行显示变量的值？

Question

我试过以下 -

我在命令提示符下创建了一个变量,如下所示 -

mysql> set @myId = 1;
Query OK, 0 rows affected (0.00 sec)

然后,要显示它,我尝试了以下没有成功 -

    mysql> show myId;
    ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that 
corresponds to your MySQL server version for the right syntax to use near 'myId' at line 1
    mysql> show @myId;
    ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use near '@myId' at line 1
    mysql> PRINT @myId;
    ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that 
corresponds to your MySQL server version for the right syntax to use near 'PRINT @myId' at line 1
    mysql> PRINT myId;
    ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that 
corresponds to your MySQL server version for the right syntax to use near 'PRINT myId' at line 1

那么我怎样才能显示出价值@myId？

Answer 1

只需SELECT像这样的变量:

SELECT @myId;

以下是有关用户定义变量的MySQL文档:

http://dev.mysql.com/doc/refman/5.5/en/user-variables.html

Answer 2

如果您正在寻找像OP一样自己设置的变量，那么@MikeBrant的答案是正确的：

SELECT @myId;

但是如果你想查看 MySQL 系统变量（这就是我来这里寻找的），那么你需要运行：

show variables like '%slow%';

或者可能：

show global variables like '%slow%';