Sql where子句中的if条件

我想从表中检索列，具体取决于条件。， 我能用的

例如，我有几个字段，即添加订单注释、取消订单注释、推迟订单注释、操作（添加、取消、推迟）和收到金额（是/否）

现在，我必须获取列添加订单注释、取消订单注释、推迟订单注释，具体取决于操作和收到的金额

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

如何在sql或plsql中完成此操作。我希望在select语句中使用此条件。请注意，通过“sql或plsql”，我假设“sql”指的是MS sql Server使用的T-sql。如果没有，请使用您的语言中相应的对等词

您需要使用语句（）

例如，在T-SQL中：

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

还要注意，在您给出的规则中，如果

amountcd

字段不是

Y

，则您将得到“Unrecogned action”作为注释。我想你可能需要澄清你的规则来防止这种情况。

试试这个

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

---

如果我正确理解了您的问题，那么实现这一点的另一种方法是执行三个单独的查询，然后将它们合并在一起

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'

---

MySQL、MS SQL Server、Oracle等？