表名：hztj

字段名：edxzqhdm ,sdxzqhdm

1.查出某一列数据中重复的，以sdxzqhdm为例

select * from hztj a where (a.sdxzqhdm) in (select sdxzqhdm from hztj group by sdxzqhdm having count(*) > 1)

2、查询出所有数据进行分组之后，和重复数据的重复次数的查询数据

select  count(sdxzqhdm) as '重复次数',sdxzqhdm from xi group by sdxzqhdm having count(*)>1 order by sdxzqhdm desc
查询及删除重复记录的方法
(1)查找表中多余的重复记录，重复记录是根据单个字段（sdxzqhdm）来判断

select * from hztj
where sdxzqhdm in (select sdxzqhdm from hztj group by sdxzqhdm having count(sdxzqhdm) > 1)
(2)删除表中多余的重复记录，重复记录是根据单个字段(sdxzqhdm）来判断，只留有rowid最小的记录

delete from hztj
where sdxzqhdm in (select sdxzqhdm from hzth group  by  sdxzqhdm having  count(sdxzqhdm) > 1)
and rowid not in (select min(rowid) from  hztj group by sdxzqhdm having count(sdxzqhdm)>1)
(3)查找表中多余的重复记录（多个字段） 

select * from hztj a
where (a.sdxzqhdm,a.edxzqhdm) in (select sdxzqhdm,edxzqhdm from hztj group by sdxzqhdm,edxzqhdm having count(*) > 1)
(4)删除表中多余的重复记录（多个字段），只留有rowid最小的记录

delete from hztj a
where (a.sdxzqhdm,a.edxzqhdm) in (select sdxzqhdm,edxzqhdm from hztj group by sdxzqhdm,edxzqhdm having count(*) > 1) 
and rowid not in (select min(rowid) from hztj group by sdxzqhdm,edxzqhdm having count(*)>1)
(5)查找表中多余的重复记录（多个字段），不包含rowid最小的记录

select * from hztj a
where (a.sdxzqhdm,a.edxzqhdm) in  (select sdxzqhdm,edxzqhdm from hztj group by sdxzqhdm,edxzqhdm having count(*) > 1)
and rowid not in (select min(rowid) from hztj group by sdxzqhdm,edxzqhdm having count(*)>1)