Question

我在使用带条件的CASE语句时面临一个小问题。基本上这是我的代码：

SELECT m.codmagazzino as Magazzino, m.integratore, i.nomeintegratore, 
m.scadenza, m.quantita,
CASE m.scadenza
when (m.scadenza <= curdate() + interval 1 month) then '50%'
when (m.scadenza >= curdate() + interval 1 month) AND (m.scadenza <= 
curdate() + interval 2 month) then '30%'
when (m.scadenza >= curdate() + interval 2 month) AND (m.scadenza <= 
curdate() + interval 3 month) then '10%'
END AS ScontoSuggerito 

FROM magazzino m INNER JOIN integratori i on m.integratore = 
i.codintegratore
order by scadenza
;

我希望它做的是检查到期日期（scadenza），并且越早过期，建议的折扣（ScontoSuggerito）就越大。问题是它给了我null，尽管有些行属于CASE语句中的条件。

                        Scadenza
2   3   Creatina Mono   2017-11-03  12  
2   5   MaxPower        2017-11-07  6   
2   9   ImpactWhey      2017-11-24  11  
2   4   Omega 3         2017-11-30  5   
1   1   IsoWhey         2018-02-17  10

Answer 1

可能只是一个语法问题：使用case语句时有两种模式：你似乎试图同时使用两种模式;当只能使用一个时。

DOCS：https://dev.mysql.com/doc/refman/5.7/en/case.html

一种模式开始case variable when valueA then ResultA when valueB then ResultB end

另一个是Case when OptionalCompoundCondition(s) then ResultA when ConditionsB then ResultB End

前者将1值与1值进行比较;后者允许复合条件。

SELECT m.codmagazzino as Magazzino
     , m.integratore
     , i.nomeintegratore
     , m.scadenza
     , m.quantita
     , CASE when (m.scadenza <= curdate() + interval 1 month) then '50%'
            when (m.scadenza >= curdate() + interval 1 month) AND (m.scadenza <= curdate() + interval 2 month) then '30%'
            when (m.scadenza >= curdate() + interval 2 month) AND (m.scadenza <= curdate() + interval 3 month) then '10%'
       END AS ScontoSuggerito 
FROM magazzino m 
INNER JOIN integratori i 
   on m.integratore = i.codintegratore
order by scadenza;

条件在select中返回null

1 个答案: