如何在 MySQL 的命令行中显示变量的值？
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How to display the value of a variable at the commandline in MySQL?
提问by CodeBlue
I tried the following -
我尝试了以下 -
I created a variable at the command prompt as follows -
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)
Then, to display it, I tried the following without success -
然后，为了显示它，我尝试了以下但没有成功 -
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
So how can I display the value of @myId?
那么如何显示 的值@myId呢？
回答by Mike Brant
Simply SELECTthe variable like this:
简单SELECT的变量是这样的：
SELECT @myId;
Here is the MySQL documentation on user-defined variables:
这是有关用户定义变量的 MySQL 文档：
回答by Ryan Shillington
If you're looking for a variable that you set yourself like the OP did, then @MikeBrant's answer is correct:
如果您正在寻找像 OP 一样为自己设置的变量，那么@MikeBrant 的答案是正确的：
SELECT @myId;
But if you want to see the MySQL system variables (which is what I came here looking for), then you need to run:
但是如果你想查看 MySQL 系统变量（这是我来这里寻找的），那么你需要运行：
show variables like '%slow%';
or possibly:
或者可能：
show global variables like '%slow%';
回答by Wilson Hauck
SHOW GLOBAL STATUS LIKE '%com_stmt%'; may be used to determine any SHOW GLOBAL STATUS current values using wildcard.
像'%com_stmt%'一样显示全局状态；可用于使用通配符确定任何 SHOW GLOBAL STATUS 当前值。
Likewise, SELECT @@thread_cache_size; may be used to display any specific SHOW GLOBAL VARIABLES current value.
同样，SELECT @@thread_cache_size; 可用于显示任何特定的 SHOW GLOBAL VARIABLES 当前值。
There are more than 300 GLOBAL STATUS values.
有超过 300 个 GLOBAL STATUS 值。
There are more than 400 GLOBAL VARIABLES with or without values. (Could be empty placeholders).
有 400 多个带或不带值的全局变量。（可能是空的占位符）。
You CAN NOT create a GLOBAL VARIABLE in MySQL.
您不能在 MySQL 中创建全局变量。
