Php 在表中查找重复项

我有一个结构如下的

messcuts

表。

id

，

student\u rollno

，

date

问题是有一些记录重复，即在同一个

日期中有两个记录具有相同的
student\u rollno
。如何移除它们？例如：

SELECT * 
FROM  `messcuts` 
WHERE student_rollno =  'b070226'

|id |student_rollno|date
|259|B070226|2011-08-06
|260|B070226|2011-08-07
|1485|B070226|2011-08-12
|1486|B070226|2011-08-13
|1487|B070226|2011-08-14
|1488|B070226|2011-08-15
|2372|B070226|2011-08-27
|2369|B070226|2011-08-24
|2368|B070226|2011-08-23
|2371|B070226|2011-08-26
|2374|B070226|2011-08-29
|2373|B070226|2011-08-28
|2370|B070226|2011-08-25
|2367|B070226|2011-08-22
|2375|B070226|2011-08-30
|2376|B070226|2011-08-31
|2938|b070226|2011-08-06

见2011-08-06，有两项记录

select student_rollno, date 
from messcuts 
group by student_rollno, date 
having count(*) > 1

并删除：

delete from messcuts d where d.id in (
    select max(s.id) 
    from messcuts as s 
    group by s.student_rollno, s.date 
    having count(*) > 1)

CREATE VIEW dups AS
SELECT MAX(id) as id
    FROM messcuts
    GROUP BY student_rollno,date
    HAVING count(*)>1

如果不在mysql中工作：

delete from messcuts 
using messcuts, messcuts as v_messcuts
where messcuts.id <> v_messcuts.id
and messcuts.student_rollno = v_messcuts.student_rollno
and messcuts.date = v_messcuts.date

从消息中删除
使用messcuts，messcuts作为v_messcuts
其中messcuts.id v_messcuts.id
和messcuts.student\u rollno=v\u messcuts.student\u rollno
和messcuts.date=v_messcuts.date

并删除：

delete from messcuts d where d.id in (
    select max(s.id) 
    from messcuts as s 
    group by s.student_rollno, s.date 
    having count(*) > 1)

CREATE VIEW dups AS
SELECT MAX(id) as id
    FROM messcuts
    GROUP BY student_rollno,date
    HAVING count(*)>1

如果不在mysql中工作：

delete from messcuts 
using messcuts, messcuts as v_messcuts
where messcuts.id <> v_messcuts.id
and messcuts.student_rollno = v_messcuts.student_rollno
and messcuts.date = v_messcuts.date

从消息中删除
使用messcuts，messcuts作为v_messcuts
其中messcuts.id v_messcuts.id
和messcuts.student\u rollno=v\u messcuts.student\u rollno
和messcuts.date=v_messcuts.date
这将显示重复项

SELECT * 
FROM messcuts
WHERE (student_rollno,date) IN
    (
    SELECT student_rollno,date
    FROM messcuts
    GROUP BY student_rollno,date
    HAVING count(*)>1
    )

DELETE FROM t2 
WHERE id IN (SELECT  id FROM dups)

并删除：

delete from messcuts d where d.id in (
    select max(s.id) 
    from messcuts as s 
    group by s.student_rollno, s.date 
    having count(*) > 1)

CREATE VIEW dups AS
SELECT MAX(id) as id
    FROM messcuts
    GROUP BY student_rollno,date
    HAVING count(*)>1

您需要多次运行此操作以消除所有重复项

SELECT * 
FROM messcuts
WHERE (student_rollno,date) IN
    (
    SELECT student_rollno,date
    FROM messcuts
    GROUP BY student_rollno,date
    HAVING count(*)>1
    )

DELETE FROM t2 
WHERE id IN (SELECT  id FROM dups)

一旦删除了重复项，最好添加一个唯一的约束来阻止进一步的问题

ALTER TABLE messcuts ADD UNIQUE std_dte (student_rollno,date)

这将显示副本

SELECT * 
FROM messcuts
WHERE (student_rollno,date) IN
    (
    SELECT student_rollno,date
    FROM messcuts
    GROUP BY student_rollno,date
    HAVING count(*)>1
    )

DELETE FROM t2 
WHERE id IN (SELECT  id FROM dups)

并删除：

delete from messcuts d where d.id in (
    select max(s.id) 
    from messcuts as s 
    group by s.student_rollno, s.date 
    having count(*) > 1)

CREATE VIEW dups AS
SELECT MAX(id) as id
    FROM messcuts
    GROUP BY student_rollno,date
    HAVING count(*)>1

您需要多次运行此操作以消除所有重复项

SELECT * 
FROM messcuts
WHERE (student_rollno,date) IN
    (
    SELECT student_rollno,date
    FROM messcuts
    GROUP BY student_rollno,date
    HAVING count(*)>1
    )

DELETE FROM t2 
WHERE id IN (SELECT  id FROM dups)

一旦删除了重复项，最好添加一个唯一的约束来阻止进一步的问题

ALTER TABLE messcuts ADD UNIQUE std_dte (student_rollno,date)

我已经编辑了这些问题。请参阅。您想删除重复项还是进行不同的选择？如何决定删除哪些？我想删除重复项。请参阅此处我已编辑了问题。请参阅。是否要删除重复项或进行不同的选择？如何决定要删除哪些？我要删除重复项。请参阅此处我要删除重复项duplicates@Shahal，明智的做法是防止php脚本插入冗余数据：），所以请按照我的答案操作。一旦没有重复项，就不必担心删除它们：）@roselan:它显示以下错误：无法在FROM子句中为update指定目标表“messcuts”。我要删除duplicates@Shahal，明智的做法是防止php脚本插入冗余数据：），所以请按照我的答案操作。一旦没有重复项，就不必担心删除它们：）@roselan:它显示了以下错误：无法在FROM子句中为更新指定目标表“messcuts”。+1，我需要解释吗；）？有些人只是在否决+1之前不阅读，我需要解释吗；）？有些人只是在投票前不读书