--例如：
id NAME VALUE
1 a pp
2 a pp
3 b iii
4 b pp
5 b pp
6 c pp
7 c pp
8 c iii
--id是主键
--要求得到这样的结果
id NAME VALUE
1 a pp
3 b iii
4 b pp
6 c pp
8 c iii
--方法1
DELETE YourTable
WHERE [id] NOT IN (SELECT MAX([id])
FROM YourTable
GROUP BY
(NAME + VALUE))
--方法2
DELETE a
FROM 表 a
LEFT JOIN (
SELECT id = MIN(id)
FROM 表
GROUP BY
NAME,
VALUE
)b
ON a.id = b.id
WHERE b.id IS NULL
--查询及删除重复记录的SQL语句
--查询及删除重复记录的SQL语句
--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)
