tryselect * from
(select a1,a2,a3 from a
union
select b1 a1,b2 a2,b3 a3 from b
union
select c1 a1,c2 a2,c3 a3
from c) t
order by a1
(select a1,a2,a3 from a
union
select b1 a1,b2 a2,b3 a3 from b
union
select c1 a1,c2 a2,c3 a3
from c) t
order by a1
也可将它作为子查询来处理