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    sql如何去重查询

    coldplay.xixicoldplay.xixi2020-10-10 11:37:29原创82

    sql去重查询的方法:重复记录根据单个字段peopleId来判断,使用语句删除,代码为【where peopleId in (select peopleId from people group by peopleId 】。

    sql去重查询的方法:

    sql 单表/多表查询去除重复记录

    单表distinct

    多表group by

    group by 必须放在 order by 和 limit之前,不然会报错

    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

    "重复记录"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
    )

    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)

    运行会产生问题,where(a.peopleId,a.seq)这样的写发是通不过的!!!

    相关学习推荐:SQL视频教程

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