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  • SQL重复记录查询(常用)

    1、查找表中多余的重复记录,重复记录是根据单个字段(peopleId)来判断
    select * from people
    where peopleId in (select   peopleId  from   people  group  by   peopleId  having  count(peopleId) > 1)

    2、删除表中多余的重复记录,重复记录是根据单个字段(peopleId)来判断,只留有rowid最小的记录
    delete from people
    where peopleId  in (select   peopleId  from people  group  by   peopleId   having  count(peopleId) > 1)
    and rowid not in (select min(rowid) from   people  group by peopleId  having count(peopleId )>1)

    3、查找表中多余的重复记录(多个字段)
    select * from vitae a
    where (a.peopleId,a.seq) in   (select peopleId,seq from vitae group by peopleId,seq  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 vitae a
    where (a.peopleId,a.seq) in   (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
    and rowid not in (select min(rowid) from vitae group by peopleId,seq 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 vitae a
    where (a.peopleId,a.seq) in   (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
    and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)
    (二)
    比方说
    在A表中存在一个字段“name”,
    而且不同记录之间的“name”值有可能会相同,
    现在就是需要查询出在该表中的各记录之间,“name”值存在重复的项;
    Select Name,Count(*) From A Group By Name Having Count(*) > 1
    如果还查性别也相同大则如下:
    Select Name,sex,Count(*) From A Group By Name,sex Having Count(*) > 1
    (三)
    方法一
    declare @max integer,@id integer
    declare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >; 1
    open cur_rows
    fetch cur_rows into @id,@max
    while @@fetch_status=0
    begin
    select @max = @max -1
    set rowcount @max
    delete from 表名 where 主字段 = @id
    fetch cur_rows into @id,@max
    end
    close cur_rows
    set rowcount 0

      方法二

      有两个意义上的重复记录,一是完全重复的记录,也即所有字段均重复的记录,二是部分关键字段重复的记录,比如Name字段重复,而其他字段不一定重复或都重复可以忽略。

      1、对于第一种重复,比较容易解决,使用
    select distinct * from tableName

      就可以得到无重复记录的结果集。

      如果该表需要删除重复的记录(重复记录保留1条),可以按以下方法删除
    select distinct * into #Tmp from tableName
    drop table tableName
    select * into tableName from #Tmp
    drop table #Tmp

      发生这种重复的原因是表设计不周产生的,增加唯一索引列即可解决。

      2、这类重复问题通常要求保留重复记录中的第一条记录,操作方法如下

      假设有重复的字段为Name,Address,要求得到这两个字段唯一的结果集
    select identity(int,1,1) as autoID, * into #Tmp from tableName
    select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoID
    select * from #Tmp where autoID in(select autoID from #tmp2)

      最后一个select即得到了Name,Address不重复的结果集(但多了一个autoID字段,实际写时可以写在select子句中省去此列)

    (四)查询重复
    select * from tablename where id in (
    select id from tablename
    group by id
    having count(id) > 1
    )

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  • 原文地址:https://www.cnblogs.com/soundcode/p/1911830.html
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