如何检查在SQL特定字段是否具有值或没有

Question

我有如下表，如果日期为null，然后我想要得到的WorkType

Empid Role WorkType1 DATE1  WorkType2 DATE2  WorkType3 DATE3 
8  P001 Work1  NULL  Work2  NULL  Work3  NULL 
9  P002 Work2  12/9/2016 Work6  NULL  Work3  NULL 
2  P003 Work3  NULL  Work6  12/9/2016 Work2  2/9/2016 
7  P004 Work4  NULL  Work6  12/9/2016 Work5  NULL 
1  P005 Work5  12/9/2016 Work4  NULL  Work3  NULL 
2  P006 Work6  NULL  Work1  12/9/2016 Work5  NULL 

Answer 1

Easiet但不是最好的解决方案是简单地计算每列中的空值，然后你可以使用这个子查询并计算总和。

select sum(case when work1_date is null then 1 else 0 end) as count_nulls_workdate1, 
      sum(case when work2_date is null then 1 else 0 end) as count_nulls_workdate2, 
      sum(case when work3_date is null then 1 else 0 end) as count_nulls_workdate3 
     from empno; 

Answer 2

试试这个：

select count(*)-count(work1_date) as count_nulls_workdate1, 
     count(*)-count(work2_date) as count_nulls_workdate2, 
     count(*)-count(work3_date) as count_nulls_workdate3 
     from Table; 

算不算空值，那么COUNT（*），其计算记录 - 计数（场）=零点

Answer 3

下面的答案是计数我对你的要求的解释，你的问题有点不清楚。

SELECT 
ID, 
EMPLOYEE, 
[ROLE], 
WorkType1, 
    CASE WHEN Date1 IS NULL THEN WorkType1 ELSE CAST(Date1 AS VARCHAR(23)) END Date1, 
WorkType2, 
    CASE WHEN Date2 IS NULL THEN WorkType2 ELSE CAST(Date2 AS VARCHAR(23)) END Date2, 
WorkType3, 
    CASE WHEN Date3 IS NULL THEN WorkType3 ELSE CAST(Date3 AS VARCHAR(23)) END Date3 
WorkType4, 
    CASE WHEN Date4 IS NULL THEN WorkType4 ELSE CAST(Date4 AS VARCHAR(23)) END Date4 

日期的显式转换为VARCHAR（23）当你用日期值这是不兼容的数据类型我选择VARCHAR（23）混合Worktype允许日期时间

根据需要在您的数据库设置中，您可能需要额外拆分日期以在输出中保留您期望的格式，下面给出了yyyy-MM-dd HH：mm：ss。

CAST(Datepart(Year,Date1) AS VARCHAR(4)) + '-'+ RIGHT('00'+CAST(Datepart(Month,Date1) AS VARCHAR(2)),2) + '-' + RIGHT('00' + CAST(Datepart(Day,Date1) AS VARCHAR(2)),2) + ' ' + RIGHT('00' + CAST(Datepart(HH,Date1) AS VARCHAR(2)),2)+ ':' + RIGHT('00'+CAST(Datepart(MINUTE,Date1) AS VARCHAR(2)),2) + ':' + RIGHT('00'+CAST(Datepart(ss,Date) AS VARCHAR(2)),2) 

我用下面的测试

DECLARE @Date1 DATEtime = '2017-01-01', @Date2 DATEtime = NULL, @Date3 Datetime = '2017-01-02' 
,@Worktype1 Varchar(20) = 'Test1' 
,@Worktype2 Varchar(20) = 'Test2' 
,@Worktype3 Varchar(20) = 'Test3' 

SELECT 
    CASE WHEN @Date1 IS NULL THEN @WorkType1 ELSE CAST(@Date1 AS VARCHAR(25)) END Date1, /*Varchar 23 date*/ 
    CASE WHEN @Date2 IS NULL THEN @WorkType2 ELSE CAST(@Date2 AS VARCHAR(25)) END Date2, /* Result of Worktype2 due to null */ 
    CASE WHEN @Date3 IS NULL THEN @WorkType3 ELSE CAST(Datepart(Year,@Date3) AS VARCHAR(4)) + '-'+ RIGHT('00'+CAST(Datepart(Month,@Date3) AS VARCHAR(2)),2) + '-' + RIGHT('00' + CAST(Datepart(Day,@Date3) AS VARCHAR(2)),2) + ' ' + RIGHT('00' + CAST(Datepart(HH,@Date3) AS VARCHAR(2)),2)+ ':' + RIGHT('00'+CAST(Datepart(MINUTE,@Date3) AS VARCHAR(2)),2) + ':' + RIGHT('00'+CAST(Datepart(ss,@Date3) AS VARCHAR(2)),2) END Date3 /* Result for Date 3 formatted to yyyy-MM-dd HH:mm:ss*/ 

其提供了以下的结果集

[结果集] [1]：https://i.stack.imgur.com/Y1uUp.jpg