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

SELECT CASE WHEN profile.nrefillno = 0 THEN 'N' ELSE 'R'END as newref
From profile

其他回答

使用SQL CASE与普通的If/Else语句一样。在下面的查询中,如果过时值=“N”或InStock值=“Y”,则输出将为1。否则,输出将为0。然后我们将0或1值放在Salable列下。

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

问题:

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

答案:

Select 
  case when p.Obsolete = 'N' 
  or p.InStock = 'Y' then 1 else 0 end as Saleable, 
  p.* 
FROM 
  Product p;

使用别名(在本例中为p)将有助于防止出现问题。

在这种情况下,案例陈述是您的朋友,采取以下两种形式之一:

简单的例子:

SELECT CASE <variable> WHEN <value>      THEN <returnvalue>
                       WHEN <othervalue> THEN <returnthis>
                                         ELSE <returndefaultcase>
       END AS <newcolumnname>
FROM <table>

扩展情况:

SELECT CASE WHEN <test>      THEN <returnvalue>
            WHEN <othertest> THEN <returnthis>
                             ELSE <returndefaultcase>
       END AS <newcolumnname>
FROM <table>

您甚至可以将case语句放在一个order by子句中进行真正的花式排序。

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