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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