比如有两个表A,B中都有xm(即姓名)字段，怎样查出两个表中有相同姓名的两个人呢？带着其它字段一起显示。我在一个表中可以实现，就是用having 过滤。可是两个表怎么办？
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SELECT *
FROM A FULL OUTER JOIN B
ON A.xm=B.xm
或者
SELECT *
FROM A FULL OUTER JOIN B
USING(xm)
或者
SELECT *
FROM A NATUREL FULL OUTER JOIN B
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select a.xm,a.filed1,b.field1 from a,b
where a.xm=b.xm
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select A.,B. from a,b
where a.xm=b.xm
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什么意思。你在一个表中能实现，那两个都实现后放到临时表里再关联不行吗？是想一句写出来吗？那可以试试嵌套子查询。
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就只有嵌套满足你的要求了！
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表A：
select * from a
where xm in (
select xm from (
select xm from a
union all
select xm from b
) as c
having count(xm)>1
)
表B：
select * from b
where xm in (
select xm from (
select xm from a
union all
select xm from b
) as c
having count(xm)>1
)