假设没有空值，您GROUP BY唯一的列，并选择最小(或最大)RowId作为要保留的行。然后，删除所有没有行id的内容:

DELETE FROM MyTable
LEFT OUTER JOIN (
   SELECT MIN(RowId) as RowId, Col1, Col2, Col3 
   FROM MyTable 
   GROUP BY Col1, Col2, Col3
) as KeepRows ON
   MyTable.RowId = KeepRows.RowId
WHERE
   KeepRows.RowId IS NULL

如果您使用的是GUID而不是整数，则可以进行替换

MIN(RowId)

with

CONVERT(uniqueidentifier, MIN(CONVERT(char(36), MyGuidColumn)))

我有一个表，需要保存不重复的行。 我不确定速度和效率。

DELETE FROM myTable WHERE RowID IN (
  SELECT MIN(RowID) AS IDNo FROM myTable
  GROUP BY Col1, Col2, Col3
  HAVING COUNT(*) = 2 )

删除重复记录

在这种情况下，大于操作符删除除第一条记录以外的所有记录

u1 FROM users u1 JOIN users u2 u1的地方。Id > u2.id 和u1.email = u2.email

<小于操作符在这种情况下删除除最后一条记录以外的所有记录

u1 FROM users u1 JOIN users u2 u1的地方。Id < u2.id 和u1.email = u2.email

有时使用软删除机制，其中记录日期以指示删除的日期。在这种情况下，可以使用UPDATE语句根据重复的条目更新该字段。

UPDATE MY_TABLE
   SET DELETED = getDate()
 WHERE TABLE_ID IN (
    SELECT x.TABLE_ID
      FROM MY_TABLE x
      JOIN (SELECT min(TABLE_ID) id, COL_1, COL_2, COL_3
              FROM MY_TABLE d
             GROUP BY d.COL_1, d.COL_2, d.COL_3
            HAVING count(*) > 1) AS d ON d.COL_1 = x.COL_1
                                     AND d.COL_2 = x.COL_2
                                     AND d.COL_3 = x.COL_3
                                     AND d.TABLE_ID <> x.TABLE_ID
             /*WHERE x.COL_4 <> 'D' -- Additional filter*/)

对于包含大约3000万行、重复量有高有低的中等数据表，这种方法非常适用。

下面的查询用于删除重复的行。本例中的表以ID作为标识列，具有重复数据的列是Column1、Column2和Column3。

DELETE FROM TableName
WHERE  ID NOT IN (SELECT MAX(ID)
                  FROM   TableName
                  GROUP  BY Column1,
                            Column2,
                            Column3
                  /*Even if ID is not null-able SQL Server treats MAX(ID) as potentially
                    nullable. Because of semantics of NOT IN (NULL) including the clause
                    below can simplify the plan*/
                  HAVING MAX(ID) IS NOT NULL) 

下面的脚本显示GROUP BY、HAVING、ORDER BY在一个查询中的用法，并返回带有重复列及其计数的结果。

SELECT YourColumnName,
       COUNT(*) TotalCount
FROM   YourTableName
GROUP  BY YourColumnName
HAVING COUNT(*) > 1
ORDER  BY COUNT(*) DESC 

通过使用下面的查询，我们可以基于单列或多列删除重复的记录。下面的查询是基于两列进行删除。表名为:testing，列名为empno,empname

DELETE FROM testing WHERE empno not IN (SELECT empno FROM (SELECT empno, ROW_NUMBER() OVER (PARTITION BY empno ORDER BY empno) 
AS [ItemNumber] FROM testing) a WHERE ItemNumber > 1)
or empname not in
(select empname from (select empname,row_number() over(PARTITION BY empno ORDER BY empno) 
AS [ItemNumber] FROM testing) a WHERE ItemNumber > 1)