Question

我有这个代码，它显示了上个月提供服务的品牌

SELECT t1.Brand, t1.ID,

DATE_FORMAT((t2.Tstamp), "%m/%e/%Y") AS "Last Serviced", 


FROM Table1 t1

INNER JOIN Table2 t2 
ON t1.ID = t2.Equip_ID

WHERE
MONTH(t2.Tstamp) <> "01"
Group by t1.ID
Order by t2.Tstamp

输出

Brand  |  ID | Last Serviced
Polo   |  1  | 12/12/2013
Shirt  |  2  | 12/24/2013

然后，如果我在品牌Polo上做另一项服务，它将在1月份插入一个新行。我想要发生的是因为我在Polo上服务然后它不再出现在列表中，列表应该是

Brand  |  ID | Last Serviced
Shirt  |  2  | 12/24/2013

我是怎么做到的？我还要添加什么？

Answer 1

您想要最近服务日期是上个月的品牌。为此，请使用having：

SELECT t1.Brand, t1.ID, DATE_FORMAT(t2.Tstamp, "%m/%e/%Y") AS "Last Serviced", 
FROM Table1 t1 INNER JOIN
     Table2 t2 
     ON t1.ID = t2.Equip_ID
Group by t1.ID
having MONTH(max(t2.Tstamp)) <> "01"
Order by t2.Tstamp;

我会在比较中包含年份和月份，但这遵循原始查询的逻辑。

编辑：

要在查询中包含年份，请将比较基于当前日期：

SELECT t1.Brand, t1.ID, DATE_FORMAT(t2.Tstamp, "%m/%e/%Y") AS "Last Serviced", 
FROM Table1 t1 INNER JOIN
     Table2 t2 
     ON t1.ID = t2.Equip_ID
Group by t1.ID
having year(max(t2.Tstamp)) <> year(now()) and
       month(max(t2.Tstamp)) <> month(now())
Order by t2.Tstamp;

Answer 2

使用 CASE 语句。我们看看：

SELECT t1.Brand, t1.ID, 
case(when MONTH(t2.Tstamp)=01 then NULL else DATE_FORMAT(t2.Tstamp, "%m/%e/%Y") end ) as `Last Serviced` 
from FROM Table1 t1 INNER JOIN Table2 t2 ON t1.ID = t2.Equip_ID 
Group by 2 Order by 3

如何不显示上个月提供服务的品牌

2 个答案: