如何在SELECT CASE中獲得有條件的小數點數

Question

它始終返回最大小數位值。在下面的例子中，它總是返回4位小數。

 SELECT 
    CASE 
    WHEN 1 = 1 THEN ISNULL(CAST(1000 AS FLOAT), -1) 
    WHEN 1 = 2 THEN ISNULL(CAST(0.00400 AS NUMERIC(13, 4)), -1) 
    ELSE ISNULL(CAST(0.00400 AS NUMERIC(13, 1)), -1) END 

Answer 1

CASE是表達式返回一個值和數據類型的所有可能的返回值必須匹配（或可隱式兼容）。

如果您想要條件小數點位置格式，請在客戶端上執行。

Answer 2

你缺少 「從源代碼」

SELECT 
    CASE 
    WHEN myvalue = 1 THEN ISNULL(CAST(1000 AS FLOAT), -1) 
    WHEN myvalue = 2 THEN ISNULL(CAST(0.00400 AS NUMERIC(13, 4)), -1) 
    ELSE ISNULL(CAST(0.00400 AS NUMERIC(13, 1)), -1) 
    END 

from ( 
select myvalue from (
select 1 as myvalue 
union 
select 2 as myvalue 
union 
select 3 as myvalue 
    union 
select null as myvalue 
) SourceTable 
) MainQueryTable 

工作正常
你只能運行這個，看看有什麼結果，你必須返回到MainSelect

select myvalue from (
    select 1 as myvalue 
    union 
    select 2 as myvalue 
    union 
    select 3 as myvalue 
    union 
select null as myvalue 
    ) SourceTable 

這將返回： myvalue
--------
NULL

請注意在CASE ISNULL THAT ISNULL（CAST（ZZZZ AS FLOAT），-1）
時myvalue的= 1，則不能爲空爲1因爲你有ELSE部分CASE