SELECT 1 AS Saleable, *
  FROM @Product
 WHERE ( Obsolete = 'N' OR InStock = 'Y' )
UNION
SELECT 0 AS Saleable, *
  FROM @Product
 WHERE NOT ( Obsolete = 'N' OR InStock = 'Y' )

SELECT  
(CASE 
     WHEN (Obsolete = 'N' OR InStock = 'Y') THEN 'YES'
                                            ELSE 'NO' 
 END) as Salable
, * 
FROM Product

使用CASE。像这样。

SELECT Salable =
        CASE Obsolete
        WHEN 'N' THEN 1
        ELSE 0
    END

通过此链接，我们可以了解T-SQL中的IF THEN ELSE：

IF EXISTS(SELECT *
          FROM   Northwind.dbo.Customers
          WHERE  CustomerId = 'ALFKI')
  PRINT 'Need to update Customer Record ALFKI'
ELSE
  PRINT 'Need to add Customer Record ALFKI'

IF EXISTS(SELECT *
          FROM   Northwind.dbo.Customers
          WHERE  CustomerId = 'LARSE')
  PRINT 'Need to update Customer Record LARSE'
ELSE
  PRINT 'Need to add Customer Record LARSE' 

这对t-SQL不够好吗？

SELECT CASE WHEN Obsolete = 'N' or InStock = 'Y' THEN 1 ELSE 0 
             END AS Saleable, * 
FROM Product

我喜欢使用CASE语句，但问题是在SQLSelect中使用IF语句。我过去使用的是：

SELECT

   if(GENDER = "M","Male","Female") as Gender

FROM ...

这就像Excel或sheets IF语句，其中有一个条件，后跟true条件，然后是false条件：

if(condition, true, false)

此外，您还可以嵌套if语句（但use应该使用CASE:-）

（注意：这在MySQL Workbench中有效，但在其他平台上可能不起作用）