如果的情況之間存在語句時條件SQL

Question

在我的存儲過程的中間，我有下面的代碼片斷：

case 
    when l.codeleasestatuscode = '5' and priorleaseid is null 
    and l.leaid in(select col1 from Waitlisthousehold) 
then '2' 
else l.codeleasestatuscode 
end 

然而，最後的條件，其中i具有從表Waitlisthousehold選擇，有一個問題。並非所有數據庫都有該表。所以我希望在表格存在時包含最後一個條件。但當我嘗試這樣做時，我收到錯誤：

case 
when l.codeleasestatuscode = '5' and priorleaseid is null 
IF EXISTS(select * from information_schema.tables where table_name='WaitlistHousehold') 
    begin 
    and l.leaid in(select col1 from Waitlisthousehold) 
    end 
then '2' 
else l.codeleasestatuscode 
end 

那麼，我該如何正確地做到這一點？

這個片段是內從語句（FROM表1上a.id = b.id和情況下，當一個連接表2 b ..）

Answer 1

你不能使得那樣的SELECT語句中添加。你可以這樣做：

IF EXISTS(select * from information_schema.tables where table_name='WaitlistHousehold') 
    BEGIN 
    SELECT whatever, 
    case 
    when l.codeleasestatuscode = '5' and priorleaseid is null 
    and l.leaid in(select col1 from Waitlisthousehold) 
    then '2' 
    else l.codeleasestatuscode 
    end AS whatever1 
    FROM wherever 
    END 
ELSE 
    BEGIN 
    SELECT whatever, 
    case 
    when l.codeleasestatuscode = '5' and priorleaseid is null 
    then '2' 
    else l.codeleasestatuscode 
    end AS whatever1 
    FROM wherever 
    END 

Answer 2

你可以有另一種情況，當你第一個內部或檢查表中存在不

CASE 
WHEN l.codeleasestatuscode = '5' and priorleaseid is null 
    CASE WHEN EXISTS(SELECT * FROM information_schema.tables WHERE table_name='WaitlistHousehold') 
     THEN 
      CASE WHEN l.leaid in(select col1 from Waitlisthousehold) THEN '2' 
      ELSE l.codeleasestatuscode END 
     ELSE '2' END   
    THEN '2'END 
ELSE l.codeleasestatuscode 
END