1.查询单列重复：
select * from test
where name in (select name from test group by name having count
(name) > 1)
2.查询多列重复：
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SELECT a.* FROM test a,(
SELECT name,code
FROM test
GROUP BY name,code
HAVING COUNT(1)>1
) AS b
WHERE a.name=b.name AND a.code=b.code
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