mysql去重复 保留一条

mysql去重复 保留一条怎么 *** 作呢？一起来看下吧：

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     peopleName IN (         SELECT             peopleName         FROM             people         GROUP BY             peopleName         HAVING             count(peopleName) > 1     ) AND peopleId NOT IN (     SELECT         min(peopleId)     FROM         people     GROUP BY         peopleName     HAVING         count(peopleName) > 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 )

6、消除一个字段的左边的第一位：

UPDATE tableName SET [ Title ]= RIGHT ([ Title ],(len([ Title ]) - 1)) WHERE     Title LIKE '村%'

7、消除一个字段的右边的第一位：

UPDATE tableName SET [ Title ]= LEFT ([ Title ],(len([ Title ]) - 1)) WHERE     Title LIKE '%村'

8、假删除表中多余的重复记录（多个字段），不包含rowid最小的记录

UPDATE vitae SET ispass =- 1 WHERE     peopleId IN (         SELECT             peopleId         FROM             vitae         GROUP BY             peopleId

select *

from table  ###

where not exists (

select * from table  ###

where # = #

and ## <##

)

在使用mysql时，有时需要查询出某个字段不重复的记录，虽然mysql提供 有distinct这个关键字来过滤掉多余的重复记录只保留一条，但往往只用它来返回不重复记录的条数，而不是用它来返回不重记录的所有值。其原因是 distinct只能返回它的目标字段，而无法返回其它字段，这个问题让我困扰了很久，用distinct不能解决的话，只有用二重循环查询来解决。

给个例子把，比如：表table_a 4条数据

id A B C D

01 ab 1a2 1b2 121

02 ab 2a3 3b3 4a1

03 ac 1a2 1b2 121

04 ac 2a4 3b2 52g

何让A字段重复取条 比

01 ab 1a2 1b2 121

03 ac 1a2 1b2 121

保留相同A值id行

select *

from table_a a

where not exists (

select 1 from table_a b

where b.A = a.A

and b.id <a.id

)

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