Question

我正在尝试编写一个查询，如果产品有任何产品信息和照片，

select
    prod.pID, prod.Manufacturer_Name, prod.pUPC, prod.pNum, prod.pPrice, prod.pSalesPrice, prod.pSalesDate, prod.pSalesEndDate, prod.pSale,
    GROUP_CONCAT(photoName) as photos
from
    ds_products as prod
    inner join ds_photos as pics on pics.objectID=prod.pID
where
   pics.photoFlag =2
group by 
   prod.pID

问题在于，没有照片的产品会被排除在结果集之外。我需要添加和/或更改哪些内容才能让照片表中未显示的产品显示在结果中？

由于

修改的

我尝试了LEFT JOIN而不是inner，但得到了相同的结果集。如果我只是运行：

select
    prod.pID, prod.Manufacturer_Name, prod.pUPC, prod.pNum, prod.pPrice, prod.pSalesPrice, prod.pSalesDate, prod.pSalesEndDate, prod.pSale
from
    ds_products as prod

我得到大约600k的结果。内部和/或左连接查询获得大约190k的结果。还有另一种方法吗？

Answer 1

使用外部联接

select
    prod.pID, prod.Manufacturer_Name, prod.pUPC, prod.pNum, prod.pPrice, prod.pSalesPrice, prod.pSalesDate, prod.pSalesEndDate, prod.pSale,
    GROUP_CONCAT(photoName) as photos
from
    ds_products as prod
    LEFT join ds_photos as pics on pics.objectID=prod.pID
where
   pics.photoFlag =2 OR pics.photoFlag is NULL
group by 
   prod.pID

我添加了一个条件，检查photoFlag对于没有相应图片的产品是否为空这是工作小提琴：http://sqlfiddle.com/#!2/c2a9c/1/0

有关详细信息：http://dev.mysql.com/doc/refman/5.0/en/outer-join-simplification.html

Answer 2

你需要像这样使用LEFT JOIN而不是INNER JOIN

select
    prod.pID, prod.Manufacturer_Name, prod.pUPC, prod.pNum, prod.pPrice, prod.pSalesPrice, prod.pSalesDate, prod.pSalesEndDate, prod.pSale,
    GROUP_CONCAT(photoName) as photos
from
    ds_products as prod
    LEFT JOIN ds_photos as pics on pics.objectID=prod.pID
group by 
   prod.pID

注意我还删除了你的where子句，因为这是在pics表中寻找一个会限制结果集的值。

mySQL union允许不匹配

2 个答案: