select *
from
(select *
from table1
union all
select *
from table2
union all
.....
from table4) aa
即在()后面给一个别名
from
(select *
from table1
union all
select *
from table2
union all
.....
from table4) aa
即在()后面给一个别名
select *
from table1
union all
select *
from table2
union all
.....
from table4