Question

嗨我有这样一张桌子：

notifies

id,user_id
1,3
2,3
3,4
4,5
5,6
6,3
7,4
8,4
9,3
10,3

我必须创建一个只对相邻行进行分组的查询

所以，这个例子的结果应该是：

user_id
3
4
5
6
3
4
3

我该怎么做？感谢

Answer 1

SELECT  user_id
FROM    notifies n
WHERE   NOT
        (
        SELECT  user_id
        FROM    notifies ni
        WHERE   ni.id < n.id
        ORDER BY
                id DESC
        LIMIT 1
        ) <=> user_id

Answer 2

我认为最好的选择是进行非常简单的选择，将结果放到某个应用程序中，然后用更合适的（命令性）语言对其进行过滤。但是，如果你需要，我的纯MySQL版本。您必须按id订购数据。

SELECT a.user_id
FROM notifies AS a
LEFT JOIN notifies AS c ON (
    SELECT MIN(id) FROM notifies AS b WHERE b.id > a.id
) = c.id
WHERE a.user_id <> c.user_id OR c.user_id IS NULL
ORDER BY a.id

第二个例子：

SELECT c.user_id
    FROM (
    SELECT a.id, a.user_id, MIN(b.id) AS next
    FROM notifies AS a
    LEFT JOIN notifies AS b ON b.id > a.id
    GROUP BY a.id, a.user_id

) AS c
LEFT JOIN notifies AS d ON d.id = c.next
WHERE c.user_id <> d.user_id OR c.next IS NULL
ORDER BY c.id

Answer 3

Select N.id, N.user_id
From notifies As N
Where Exists    (
                Select 1
                From notifies As N2
                Where N2.id = N.id + 1
                    And N2.user_id <> N.user_id
                )

Answer 4

试试这个：

选择通知表，并使用ROW_NUMBER（）命令放置行号，按id排序（称之为id_no）
使用行号创建子选择查询（称之为prev_id_no），但仅选择上一行（其中prev_id_no =（id_no - 1））
将上面的两个select语句嵌套在SELECT * FROM（）下，以便您可以操作row_numbers
创建一个列，用于评估＃1 user_id是否等于＃2 user_id。使用“CASE THEN'YES ELSE'NO'AS [DUPLICATE]”
将最终结果表从＃3嵌套并按DUPLICATE ='NO'

SQL是这样的：

SELECT [user_id] FROM (
    SELECT *,
    CASE WHEN (
        SELECT [user_id] FROM (
            SELECT ROW_NUMBER() OVER(ORDER BY id) AS [prev_id_no], 
            [user_id]

            FROM notifies
        ) FILTER_IN

        WHERE FILTER_IN.prev_id_no = (FILTER_OUT.id_no - 1)
    ) = FILTER_OUT.[user_id] THEN 'YES' ELSE 'NO' END AS [DUPLICATE]

    FROM (
        SELECT ROW_NUMBER() OVER(ORDER BY id) AS [id_no], 
        [user_id]

        FROM notifies
    ) FILTER_OUT
) FILTER_FINAL

WHERE FILTER_FINAL.DUPLICATE = 'NO'

结果是：

user_id
3
4
5
6
3
4
3

仅对相邻行进行分组

4 个答案: