如果條件在哪裏條款

Question

我想從表中檢索列，根據條件。， 我可以使用。

例如，我已經領域，即爲了添加註釋，取消訂單的意見，推遲訂單註釋，操作（添加，取消，推遲）和收到的金額（Y/N）

現在我來取列添加秩序的意見，取消訂單的意見，推遲訂單註釋根據行動和收到的款項，

if(action='add' and amount received='Y') 
then 
i've to fetch add order comments column 
elseif(action='postpone' and amount received='Y') 
then 
i've to fetch postpone order comments column 
else (action='cancel') 
then i've to fetch cancel order comments 

如何得到這個SQL或PLSQL做，我想這個條件在SELECT語句

Answer 1

請注意，通過「sql或plsql」我假設「sql」是指MS SQL Server使用的T-SQL。如果沒有，請使用您的語言的相應等效語言。

您需要使用CASE (T-SQL)聲明（PL-SQL equivalent）

例如，在T-SQL：

SELECT OrderId AS OrderId 
     CASE 
      WHEN Action = 'add' AND amountRcd = 'Y' THEN addOrderComment 
      WHEN Action = 'postpont' AND amountRcd = 'Y' THEN postponeOrderComment 
      WHEN Action = 'cancel' THEN cancelOrderComment 
      ELSE 'Unrecognised action' 
     END AS Comment 
FROM tblOrders 

還要注意的是，在你給的規則，如果amountRcd字段不是Y，那麼你會得到「無法識別的行動」作爲評論。我想你可能需要澄清你的規則，以防止這種情況。

Answer 2

試試這個

select order comment case when action ='add' 
    and amount received ='y' 
    else select postpone order comments when action ='postpone' 
    and amount received='y' 
    else select cancel when action ='cancel' end 
    from table 

Answer 3

如果我理解正確的問題，那麼實現這一點的另一種方式是執行三個獨立的查詢，然後聯合在一起。

select orderID as OrderID, addOrderComments as Comment 
from tblOrders 
where Action = 'add' AND amountRcd = 'Y' 
union 
select orderID as OrderID, postponeOrderComment as Comment 
from tblOrders 
where Action = 'postpone' AND amountRcd = 'Y' 
union 
select orderID as OrderID, cancelOrderComment as Comment 
from tblOrders 
where Action = 'cancel'