如何在SQL SELECT中执行IF ... THEN？ [英] How do I perform an IF...THEN in an SQL SELECT?

问题描述

如何在 SQL SELECT 声明中执行 IF ...那么？

例如：

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

推荐答案

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

The CASE statement is the closest to IF in SQL and is supported on all versions of SQL Server

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

你只需要做 CAST 如果你想把结果作为一个布尔值，如果你对 int 感到满意，这可行：

You only need to do the CAST if you want the result as a boolean value, if you are happy with an int, this works:

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，甚至包含在聚合中。

CASE statements can be embedded in other CASE statements and even included in aggregates.

SQL Server Denali（SQL Server 2012）添加 IIF 声明，也可在访问 :(由 Martin Smith ）

SQL Server Denali (SQL Server 2012) adds the IIF statement which is also available in access: (pointed out by Martin Smith)

SELECT IIF(Obsolete = 'N' or InStock = 'Y', 1, 0) as Saleable, * FROM Product

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