Question

我有一个查询，从满足条件的表中选择列，问题是这个逻辑重复多次（每个列需要一次），并想知道是否有更好的方法。

SELECT
  CASE 
    WHEN (date1 IS NULL) THEN [date2]       
    WHEN (date1 IS NOT NULL OR ( date1 IS NOT NULL AND date2 IS NOT NULL )) THEN [date1]
    ELSE ''
  END AS selectedDate

//Repeat above statement for [day], [hour], [minute]

我想知道是否可以在具有单独别名的同一语句下聚合多个这些case语句，因为它们都依赖于相同的条件而不是为每列重复多次相同的语句，例如我试过以下内容：

SELECT
  CASE 
    WHEN (date1 IS NULL) THEN [date2] as "selectedDate", [day2] as "day", [hour2] as "hour", [minute2] as "minute"  
    WHEN (date1 IS NOT NULL OR ( date1 IS NOT NULL AND date2 IS NOT NULL )) THEN [date1] as "selectedDate", [day1] as "day", [hour1] as "hour", [minute1] as "minute"   
    ELSE ''

Answer 1

不是你描述的方式......

另一种方法是使用isnull()或coalesce()：

select 
    SelectedDate = coalesce(date1,date2)
  , [Day]        = coalesce(day1,day2)
  , [Hour]       = coalesce(hour1,hour2)
  , [Minute]     = coalesce(minute1,minute2)
from t

Answer 2

没有。每列都需要自己的select语句。

对于此CASE声明的特定应用，您可能正在使用COALESCE。

SELECT COALESCE(date1, date2) AS selectedDate FROM SomeTable

TSQL - CASE WHEN语句的多个别名

2 个答案: