如何在 SQL Server 的结果中删除返回“Null”的行答案

【问题标题】：How to remove the rows that returns 'Null' in the results in SQL Server如何在 SQL Server 的结果中删除返回“Null”的行
【发布时间】：2021-08-10 19:59:58
【问题描述】：

我有一个查询，可以根据需要为我提供结果。但我不希望在最终结果中显示“Null”的行。

SELECT DISTINCT In_Time, 
    Out_Time,
    "Duration" = CASE
                    WHEN DATEDIFF (hh,In_Time, Out_Time) >= 2 
                       THEN 'Duration was GREATER than 2 hours'
                 END  
FROM 
    CASES  C

显示的结果：

In_Time	Out_Time	Duration
2021-04-01 09:05:21	2021-04-01 09:28:46	NULL
2021-04-01 09:31:37	2021-04-01 10:33:27	NULL
2021-04-01 08:56:00	2021-04-01 11:46:11	duration was GREATER than 2 hours
2021-04-02 12:50:00	2021-04-02 14:52:26	duration was GREATER than 2 hours
2021-04-02 16:10:57	2021-04-02 17:05:21	NULL

如何删除返回null的行并得到如下结果

预期结果：

In_Time	Out_Time	Duration
2021-04-01 08:56:00	2021-04-01 11:46:11	duration was GREATER than 2 hours
2021-04-02 12:50:00	2021-04-02 14:52:26	duration was GREATER than 2 hours

【问题讨论】：

标签： sql sql-server-2012

【解决方案1】：

也许最简单的方法就是为此添加一个WHERE 子句：

WHERE DATEDIFF (hh,In_Time, Out_Time) >= 2

而在原来的SQL中：

SELECT DISTINCT In_Time, 
        Out_Time,
        CASE
          WHEN DATEDIFF (hh,In_Time, Out_Time) >= 2 THEN 'Duration was GREATER than 2 hours'
        END AS [Duration]
  FROM  CASES C 
  WHERE DATEDIFF (hh,In_Time, Out_Time) >= 2

【讨论】：

【解决方案2】：

我建议：

SELECT DISTINCT In_Time, Out_Time,
      'Duration was GREATER than 2 hours' as Duration
FROM CASES C 
WHERE DATEDIFF(hour, In_Time, Out_Time) >= 2;

不过，包含字符串 SELECT 似乎是多余的，因为所有值都相同。

另一种方法是将DURATION 的定义放在FROM 子句中，这样您就可以在多个地方使用该值：

SELECT DISTINCT c.In_Time, c.Out_Time, v.Duration
FROM CASES C CROSS APPLY
     (VALUES (CASE WHEN DATEDIFF(hour, c.In_Time, c.Out_Time) >= 2
                   THEN 'Duration was GREATER than 2 hours'
              END)
     ) v(Duration)
WHERE v.Duration IS NOT NULL;

【讨论】：

【解决方案3】：

感谢您的回答。

当我使用以下查询时，我得到了答案

SELECT DISTINCT In_Time, 
    Out_Time,
    "Duration" = 
    CASE
WHEN DATEDIFF (hh,In_Time, Out_Time) >= 2 THEN 'Duration was GREATER than 2 hours'
    END  
    FROM CASES  C
WHERE DATEDIFF(hour, In_Time, Out_Time) >= 2

【讨论】：