如果发现连续的 NULL，则将行删除到第 n 个位置答案

【问题标题】：Remove rows to the nth position if it found continuous NULL如果发现连续的 NULL，则将行删除到第 n 个位置
【发布时间】：2021-06-03 16:10:01
【问题描述】：

我正面临需要帮助的情况。我使用的是 SQL Server 2014。

我的查询是我必须删除 NULL 值的行，但前提是它从一开始就连续找到，如下所示，我给出了一些输入和输出示例。

Sample Input 1 :

Sample Output 1 :

Sample Input 2 :

Sample Output 2: (because from the starting it doesn't have null values. Null values are in the middle)

Sample Input 3:

Sample Output 3: (it will return blank table as all the null values get removed)

提前致谢。

【问题讨论】：

如果有 2 个起始空值，然后是一个值，然后是另一个空值怎么办？您只想删除第一个空值吗？
你所说的“从一开始”是什么意思？特定日期的第一个条目，特定用户的第一个实例？？
@JaviTorre 只有 StartTime 可以有 NULL 值。因此，如果有 2 条记录并且在 StartTime 中都具有 NULL，那么都应该删除它们，但是如果第一行没有 NULL，而第二行有 NULL，那么它会按原样显示。（参见示例输入和输出 2）。
如果 1,2,4 不为空，6 为空怎么办？
@PankajSanwal “从开始”是指第 1 行到第 n 行，它将在 StartTime 中获得 NULL，但只能连续。如果在第 3 行 StartTime 中不为空，那么它将删除开始的 2 行，因为两行都为空。

标签： sql sql-server database tsql

【解决方案1】：

这不是 SQL Server，但可能会提示您如何继续。计算排序的空值（如果为空，则求和 0），然后去掉那些为 0 的值。

with aux (id, v) as (
    select 1, null from dual union all
    select 2, null from dual union all
    select 3, 2 from dual union all
    select 4, null from dual union all
    select 5, 2 from dual),
aux1 as (
    SELECT
        a.*,
        SUM(
            CASE
                WHEN v IS NULL THEN
                    0
                ELSE
                    1
            END
        ) OVER(
        ORDER BY
            id
        ) h1
    FROM
        aux a
)
SELECT
    *
FROM
    aux1
where h1>0;

输出：

ID  V   H
---------
3   2   1
4       1
5   2   2

【讨论】：

from dual 不是 SQL Server 语法

【解决方案2】：

您可以尝试以下方法。您可以在 SSMS 中运行每个场景。

场景一

DECLARE @data table ( InstanceID int, [TimeStamp] datetime, StartTime datetime );
INSERT INTO @data VALUES
    ( 1, '08/22/2020 07:06:00', NULL ), 
    ( 2, '08/22/2020 12:30:00', NULL ), 
    ( 4, '08/22/2020 14:32:00', NULL ), 
    ( 6, '08/22/2020 17:13:00', '08/22/2020 17:30:00' );

WITH cte AS (
    SELECT
        ROW_NUMBER() OVER ( ORDER BY [TimeStamp] ) AS id,
        InstanceID,
        [TimeStamp],
        StartTime
    FROM @data
)
SELECT
    InstanceID, [TimeStamp], StartTime
FROM cte
OUTER APPLY (

    SELECT CASE 
        WHEN cte.id = 1 AND cte.StartTime IS NULL THEN 1
        WHEN cte.id = 1 AND cte.StartTime IS NOT NULL THEN 0
        WHEN cte.StartTime IS NULL AND ( SELECT COUNT ( * ) FROM cte AS c WHERE c.id < cte.id AND c.StartTime IS NOT NULL ) > 0 THEN 0
        WHEN cte.StartTime IS NOT NULL THEN 0
        ELSE 1
    END AS Exclude

) AS x
WHERE
    Exclude = 0
ORDER BY
    [TimeStamp];

+------------+-------------------------+-------------------------+
| InstanceID |        TimeStamp        |        StartTime        |
+------------+-------------------------+-------------------------+
|          6 | 2020-08-22 17:13:00.000 | 2020-08-22 17:30:00.000 |
+------------+-------------------------+-------------------------+

场景二

DECLARE @data table ( InstanceID int, [TimeStamp] datetime, StartTime datetime );
INSERT INTO @data VALUES
    ( 1, '08/22/2020 07:06:00', '08/22/2020 07:06:00' ), 
    ( 2, '08/22/2020 12:30:00', NULL ), 
    ( 4, '08/22/2020 14:32:00', NULL ), 
    ( 6, '08/22/2020 17:13:00', '08/22/2020 17:30:00' );

WITH cte AS (
    SELECT
        ROW_NUMBER() OVER ( ORDER BY [TimeStamp] ) AS id,
        InstanceID,
        [TimeStamp],
        StartTime
    FROM @data
)
SELECT
    InstanceID, [TimeStamp], StartTime
FROM cte
OUTER APPLY (

    SELECT CASE 
        WHEN cte.id = 1 AND cte.StartTime IS NULL THEN 1
        WHEN cte.id = 1 AND cte.StartTime IS NOT NULL THEN 0
        WHEN cte.StartTime IS NULL AND ( SELECT COUNT ( * ) FROM cte AS c WHERE c.id < cte.id AND c.StartTime IS NOT NULL ) > 0 THEN 0
        WHEN cte.StartTime IS NOT NULL THEN 0
        ELSE 1
    END AS Exclude

) AS x
WHERE
    Exclude = 0
ORDER BY
    [TimeStamp];

+------------+-------------------------+-------------------------+
| InstanceID |        TimeStamp        |        StartTime        |
+------------+-------------------------+-------------------------+
|          1 | 2020-08-22 07:06:00.000 | 2020-08-22 07:06:00.000 |
|          2 | 2020-08-22 12:30:00.000 | NULL                    |
|          4 | 2020-08-22 14:32:00.000 | NULL                    |
|          6 | 2020-08-22 17:13:00.000 | 2020-08-22 17:30:00.000 |
+------------+-------------------------+-------------------------+

场景三

DECLARE @data table ( InstanceID int, [TimeStamp] datetime, StartTime datetime );
INSERT INTO @data VALUES
    ( 1, '08/22/2020 07:06:00', NULL ), 
    ( 2, '08/22/2020 12:30:00', NULL ), 
    ( 4, '08/22/2020 14:32:00', NULL );

WITH cte AS (
    SELECT
        ROW_NUMBER() OVER ( ORDER BY [TimeStamp] ) AS id,
        InstanceID,
        [TimeStamp],
        StartTime
    FROM @data
)
SELECT
    InstanceID, [TimeStamp], StartTime
FROM cte
OUTER APPLY (

    SELECT CASE 
        WHEN cte.id = 1 AND cte.StartTime IS NULL THEN 1
        WHEN cte.id = 1 AND cte.StartTime IS NOT NULL THEN 0
        WHEN cte.StartTime IS NULL AND ( SELECT COUNT ( * ) FROM cte AS c WHERE c.id < cte.id AND c.StartTime IS NOT NULL ) > 0 THEN 0
        WHEN cte.StartTime IS NOT NULL THEN 0
        ELSE 1
    END AS Exclude

) AS x
WHERE
    Exclude = 0
ORDER BY
    [TimeStamp];

+------------+-----------+-----------+
| InstanceID | TimeStamp | StartTime |
+------------+-----------+-----------+

【讨论】：

【解决方案3】：

/* scenario 1 */
declare @t table ( InstanceID int, [TimeStamp] datetime, StartTime datetime );
insert into @t values
    ( 1, '08/22/2020 07:06:00', null ), 
    ( 2, '08/22/2020 12:30:00', null ), 
    ( 4, '08/22/2020 14:32:00', null ), 
    ( 6, '08/22/2020 17:13:00', '08/22/2020 17:30:00' );

with t_cte as (
    select *,
           row_number() over (order by InstanceID) rn,
           sum(case when StartTime is null then 1 else 0 end) over (order by InstanceID) is_null
    from @t)
select *
from @t t
where not exists(select * 
                 from t_cte tc
                 where tc.InstanceID=t.InstanceID
                       and rn=is_null);

InstanceID  TimeStamp                   StartTime
6           2020-08-22 17:13:00.000     2020-08-22 17:30:00.000

/* scenario 2 */
declare @t table ( InstanceID int, [TimeStamp] datetime, StartTime datetime );
insert into @t values
    ( 1, '08/22/2020 07:06:00', '08/22/2020 07:06:00' ), 
    ( 2, '08/22/2020 12:30:00', null ), 
    ( 4, '08/22/2020 14:32:00', null ), 
    ( 6, '08/22/2020 17:13:00', '08/22/2020 17:30:00' );

with t_cte as (
    select *,
           row_number() over (order by InstanceID) rn,
           sum(case when StartTime is null then 1 else 0 end) over (order by InstanceID) is_null
    from @t)
select *
from @t t
where not exists(select * 
                 from t_cte tc
                 where tc.InstanceID=t.InstanceID
                       and rn=is_null);

InstanceID  TimeStamp                   StartTime
1           2020-08-22 07:06:00.000     2020-08-22 07:06:00.000
2           2020-08-22 12:30:00.000     NULL
4           2020-08-22 14:32:00.000     NULL
6           2020-08-22 17:13:00.000     2020-08-22 17:30:00.000

/* scenario 3 */
declare @t table ( InstanceID int, [TimeStamp] datetime, StartTime datetime );
insert into @t values
    ( 1, '08/22/2020 07:06:00', null ), 
    ( 2, '08/22/2020 12:30:00', null ), 
    ( 4, '08/22/2020 14:32:00', null ), 
    ( 6, '08/22/2020 17:13:00', null );

with t_cte as (
    select *,
           row_number() over (order by InstanceID) rn,
           sum(case when StartTime is null then 1 else 0 end) over (order by InstanceID) is_null
    from @t)
select *
from @t t
where not exists(select * 
                 from t_cte tc
                 where tc.InstanceID=t.InstanceID
                       and rn=is_null);

no rows returned

【讨论】：

【解决方案4】：

注意：取消注释您要测试的示例。

试试这个：

DECLARE @SampleTable    TABLE 
        (InstanceID int, TStamp datetime, StartTime datetime)
;
INSERT INTO @SampleTable
VALUES  
/**/
        (1, '8/22/2020 07:06', NULL)
    ,   (2, '8/22/2020 12:30', NULL)
    ,   (4, '8/22/2020 14:32', NULL)
    ,   (6, '8/22/2020 17:13', '8/22/2020 17:13')

/*
        (1, '8/22/2020 07:06', '8/22/2020 07:06')
    ,   (2, '8/22/2020 12:30', NULL)
    ,   (4, '8/22/2020 14:32', NULL)
    ,   (6, '8/22/2020 17:13', '8/22/2020 17:13')
*/
/*
        (1, '8/22/2020 07:06', NULL)
    ,   (2, '8/22/2020 12:30', NULL)
    ,   (4, '8/22/2020 14:32', NULL)
*/
;
DECLARE @FirstInstanceIsNull bit 
    =   CASE WHEN (
                    SELECT  TOP 1 StartTime 
                    FROM    @SampleTable 
                    ORDER BY InstanceID
                 ) IS NULL 
            THEN 1 
            ELSE 0 
        END
;
SELECT  *
FROM    @SampleTable
WHERE   (@FirstInstanceIsNull = 0 )
    OR  (@FirstInstanceIsNull = 1 AND StartTime IS NOT NULL)

【讨论】：