Mysql异常：Every derived table must have its own alias

Mysql错误：Every derived table must have its own alias mysql执行多表查询时报错： [SQL] SELECT * from (select e.account from employee eUNIONSELECT u.account from `user` uUNIONSELECT a.account from agent a)[Err] 1248 - Every derived table mus

Mysql错误：Every derived table must have its own alias

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。