如何在MySQL中制作/使用变量

本文介绍了如何在MySQL中制作/使用变量的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我知道在MySQL中您可以执行类似SELECT foo AS bar FROM TABLE t;的操作，而我正在尝试执行SELECT command1 FROM table1 AS foo, command2 FROM table2 AS bar, (foo-bar) AS difference;的操作，但是MySQL不允许我这样做.有没有办法在MySQL中做到这一点，或者我需要扩展一下吗?提前致谢！

I know that in MySQL you can do something like SELECT foo AS bar FROM TABLE t; I'm trying to do something to the effect of SELECT command1 FROM table1 AS foo, command2 FROM table2 AS bar, (foo-bar) AS difference; but MySQL doesn't let me do that. Is there a way to do this in MySQL or will I need to get some extension? Thanks in Advance!

架构

create table t1
(   id int auto_increment primary key,
    thing varchar(100) not null
);

create table t2
(   id int auto_increment primary key,
    descr varchar(100) not null
);

insert t1(thing) values ('cat'),('dog');
insert t2(descr) values ('meow'),('likes bones');

查询

select t1.thing,t2.descr into @var1,@var2 
from t1 
join t2 
on t2.id=t1.id 
where t1.id=2; -- to avoid Error 1172: Result consisted of more than one row

查看vars

select @var1 as thing,@var2 as descr;
+-------+-------------+
| thing | descr       |
+-------+-------------+
| dog   | likes bones |
+-------+-------------+

像上面一样选择var的重要部分是将结果集限制为最多1行.

The important part of selecting into vars like above is to limit the resultset to 1 row max.

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