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Mysql错误:Every derived table must have its own alias

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mysql执行多表查询时报错:

[SQL] SELECT * from 
(
select e.account from employee e
UNION
SELECT u.account from `user` u
UNION
SELECT a.account from agent a
)

[Err] 1248 - Every derived table must have its own alias

这句话的意思是每个派生出来的表必须有一个自己的别名

 

一般是在多表查询或者子查询的时候会出现这个错误,因为在嵌套查询中,子查询的结果是作为一个派生表给上一级进行查询,所以子查询的结果必须有一个别名。

 

上面的例子中,把查询语句修改一下:

SELECT * from 
(
select e.account from employee e
UNION
SELECT u.account from `user` u
UNION
SELECT a.account from agent a
)as total

如上所示,在子查询的后面增加一句 as total,相当于给子查询的结果集派生表取别名为total,问题就解决了。

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