在SQL Server中做嵌套case语句逻辑的最佳方法

我正在写一个SQL查询，其中一些返回的列需要根据相当多的条件计算。

我目前使用嵌套的case语句，但它变得混乱。有没有更好的(更有条理和/或更易读的)方式?

(我使用的是Microsoft SQL Server, 2005)

一个简单的例子:

SELECT
    col1,
    col2,
    col3,
    CASE
        WHEN condition 
        THEN
            CASE
                WHEN condition1 
                THEN
                    CASE 
                        WHEN condition2
                        THEN calculation1
                        ELSE calculation2
                    END
                ELSE
                    CASE 
                        WHEN condition2
                        THEN calculation3
                        ELSE calculation4
                    END
            END
        ELSE 
            CASE 
                WHEN condition1 
                THEN 
                    CASE
                        WHEN condition2 
                        THEN calculation5
                        ELSE calculation6
                    END
                ELSE
                    CASE
                        WHEN condition2 
                        THEN calculation7
                        ELSE calculation8
                    END
            END            
    END AS 'calculatedcol1',
    col4,
    col5 -- etc
FROM table

当前回答

把所有这些案子合并在一起。

SELECT
    col1,
    col2,
    col3,
    CASE
        WHEN condition1 THEN calculation1 
        WHEN condition2 THEN calculation2
        WHEN condition3 THEN calculation3
        WHEN condition4 THEN calculation4
        WHEN condition5 THEN calculation5
        ELSE NULL         
    END AS 'calculatedcol1',
    col4,
    col5 -- etc
FROM table

2012-07-12 17:17:23

其他回答

你可以结合多个条件来避免这种情况:

CASE WHEN condition1 = true AND condition2 = true THEN calculation1 
     WHEN condition1 = true AND condition2 = false THEN calculation2
     ELSE 'what so ever' END,

2013-05-31 11:45:43

把所有这些案子合并在一起。

SELECT
    col1,
    col2,
    col3,
    CASE
        WHEN condition1 THEN calculation1 
        WHEN condition2 THEN calculation2
        WHEN condition3 THEN calculation3
        WHEN condition4 THEN calculation4
        WHEN condition5 THEN calculation5
        ELSE NULL         
    END AS 'calculatedcol1',
    col4,
    col5 -- etc
FROM table

2012-07-12 17:17:23

这个例子可能对你有帮助，图中显示了当有if和多个内部if循环时SQL case语句的样子

2019-06-24 10:14:52

你可以尝试一些COALESCE技巧，例如:

SELECT COALESCE(
  CASE WHEN condition1 THEN calculation1 ELSE NULL END,
  CASE WHEN condition2 THEN calculation2 ELSE NULL END,
  etc...
)

2009-02-03 01:44:10

下面是嵌套的"Complex" case语句的简单解决方案: ——嵌套Case复杂表达式

select  datediff(dd,Invdate,'2009/01/31')+1 as DaysOld, 
    case when datediff(dd,Invdate,'2009/01/31')+1 >150 then 6 else
        case when datediff(dd,Invdate,'2009/01/31')+1 >120 then 5 else 
            case when datediff(dd,Invdate,'2009/01/31')+1 >90 then 4 else 
                case when datediff(dd,Invdate,'2009/01/31')+1 >60 then 3 else 
                    case when datediff(dd,Invdate,'2009/01/31')+1 >30 then 2 else 
                        case when datediff(dd,Invdate,'2009/01/31')+1 >30 then 1 end 
                    end
                end
            end
        end
    end as Bucket
from rm20090131atb

只要确保每个case语句都有一个结束语句

2009-07-17 14:13:01

在SQL Server中做嵌套case语句逻辑的最佳方法

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