我正在尝试创建一个sql语句，其中我希望根据条件显示列。我尝试了以下方法：

IF (T0."Confirmed" = "Y") 
  BEGIN
SELECT T0."DocNum",T1."VisOrder", T1."Quantity", T1."Price", T0."CardCode", T0."CardName", T1."OpenCreQty", T0."CreateDate", T0."Printed", T0."Confirmed", T0."U_ACM_O_ETD", T2."DocDate", T0."U_ACM_O_LOS" 
FROM OPOR T0  INNER JOIN POR1 T1 ON T0."DocEntry" = T1."DocEntry", OWTQ T2   
  END
ELSE     
  BEGIN 
SELECT T0."DocNum",T1."VisOrder", T1."Quantity", T1."Price", T0."CardCode", T0."CardName", T1."OpenCreQty", T0."CreateDate", T0."Printed", T0."Confirmed", T0."U_ACM_O_ETD", T2."DocDate", T0."U_ACM_O_LOS" 
FROM OPOR T0  INNER JOIN POR1 T1 ON T0."DocEntry" = T1."DocEntry", OWTQ T2
  END

但是当我尝试运行它时，它告诉我if语句附近有一个不正确的语法。
[sap ag][libodbchdb dll][hdbodbc]语法错误或访问冲突；257 sql语法错误：“if”附近语法不正确：第1行第1列（ecm2）（位置1）
更新：
我更新了密码

select
      case 
        when T2."Confirmed" = 'Y' then
            (SELECT T0."DocNum", T0."CardCode", T0."CardName", T0."NumAtCard", 
               T1."DocDate", T1."ReqDate", T0."U_ACM_ORDERINFO", T2."DocNum", 
               T2."CardCode", T2."CardName", T2."U_ACM_CONTAINERLOAD", 
               T2."U_ACM_O_ETD", T2."U_ACM_A_ETD", T2."Confirmed" 
             FROM ORDR T0 , OPRQ T1, OPOR T2)
        when T2."Confirmed" = 'N' then
            (SELECT T0."DocNum", T0."CardCode", T0."CardName", T0."NumAtCard", 
               T1."DocDate", T1."ReqDate", T0."U_ACM_ORDERINFO", T2."DocNum", 
               T2."CardCode", T2."CardName", T2."U_ACM_CONTAINERLOAD", 
               T2."U_ACM_O_ETD", T2."Confirmed" 
             FROM ORDR T0 , OPRQ T1, OPOR T2)
     end

更新的错误
[sap ag][libodbchdb dll][hdbodbc]语法错误或访问冲突；257 sql语法错误：第8行第1列“”（ecm2）（位置693）
希望你们能指出我做错了什么。