Question

我有一个如下所示的表格结构

FileId      FileName          CreatedBy       CreationDate

-------    ----------        -----------      ------------
File1_1    File1                User1        2014/09/12 17:10:49
File1_2    File1                User1        2014/09/11 17:45:49
File2_1    File2                User2        2014/05/11 17:45:22
File2_3    File2                User1        2014/08/11 17:47:22

我想编写一个查询，它将获取名称中包含重复条目的文件，并删除所有条目但是具有最新日期的条目。例如，在当前示例中，它将删除标识为File1_2和File2_1

的记录

Answer 1

从SELECT查询开始，该查询标识要删除的行。

SELECT y.CreatedBy, y.FileId, y.FileName, y.CreationDate
FROM YourTable AS y
WHERE
    y.CreationDate <  
        DMax(
            "CreationDate",
            "YourTable",
            "FileName='" & y.FileName & "'"
            );

验证查询是否标识了正确的行后，将其转换为DELETE查询。

DELETE
FROM YourTable AS y
WHERE
    y.CreationDate <  
        DMax(
            "CreationDate",
            "YourTable",
            "FileName='" & y.FileName & "'"
            );

Answer 2

DELETE TableA 
FROM TableA A
INNER JOIN (
SELECT MAX(creationDate) as dt, FileId FROM TableA
GROUP by FileId
HAVING count(*) > 1
) T
where A.FileId = T.FileId
and A.dt < T.dt

从表中查找重复记录并删除除最新日期之外的所有记录

2 个答案: