每一个派生表都必须给其取个别名
如:
select * from (select * from table_a union
select * from table_b
)
解决办法:
select * from ( select * from table_a union select * from table_b ) c
解决办法:
select * from ( select * from table_a union select * from table_b ) c
如果不加上这个别名,就会出现异常