t1表:
country area
a 11
e 22
f 33
g 44t2表:
country area
a 1
b 2
c 3
d 4
我现在要把两表的信息组合起来,相同的国家只显示一条记录(也就是屏蔽另一条记录),应当如何控制他显示哪一个表的内容?
country area
a 11
e 22
f 33
g 44t2表:
country area
a 1
b 2
c 3
d 4
我现在要把两表的信息组合起来,相同的国家只显示一条记录(也就是屏蔽另一条记录),应当如何控制他显示哪一个表的内容?
from t1
union all
select *
from t2 a
where not exists(select 1 from t1 where country = a.country)
from (
select * from t1
unoion all
select * from t2) b
group by b.country
select * from t1
union all
select * from t2 where country not in (select country from t1)