如何在SQL SELECT语句中执行IF…THEN?

例如:

SELECT IF(Obsolete = 'N' OR InStock = 'Y' ? 1 : 0) AS Saleable, * FROM Product

当前回答

Microsoft SQL Server(T-SQL)

在选择中,使用:

select case when Obsolete = 'N' or InStock = 'Y' then 'YES' else 'NO' end

在where子句中,使用:

where 1 = case when Obsolete = 'N' or InStock = 'Y' then 1 else 0 end

其他回答

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' )

CASE语句最接近SQL中的IF,并且在所有版本的SQL Server上都受支持。

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

如果希望结果为布尔值,则只需使用CAST运算符。如果您对int感到满意,这将起作用:

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

CASE语句可以嵌入到其他CASE语句中,甚至可以包含在聚合中。

SQL Server Denali(SQL Server 2012)添加了IIF语句,该语句也可用于访问(Martin Smith指出):

SELECT IIF(Obsolete = 'N' or InStock = 'Y', 1, 0) as Saleable, * FROM Product
case statement some what similar to if in SQL server

SELECT CASE 
            WHEN Obsolete = 'N' or InStock = 'Y' 
               THEN 1 
               ELSE 0 
       END as Saleable, * 
FROM Product
SELECT CASE WHEN Obsolete = 'N' or InStock = 'Y' THEN 1 ELSE 0 
             END AS Saleable, * 
FROM Product
SELECT
if((obsolete = 'N' OR instock = 'Y'), 1, 0) AS saleable, *
FROM
product;