Question

我有3张桌子

warehouse(id,name)
article (id, name)
inventory(id,warehouse_id,article_id, quantity)

在文章中我有1000篇文章，我有4个仓库。现在在我的表库存中，我只有300个关节的记录，只有2个仓库。我想用他们所有的仓库获得所有文章，但我只能获得300行。我正在尝试离开加入，但我无法得到它。

For example i want this
article 1: 
warehouse 1:1000
warehouse 2:1000
warehouse 3:0  (beacuse there is no record in invetory)
warehouse 4:3000

article 2:  
warehouse 1:0 (beacuse there is no record in invetory)
warehouse 2:0 (beacuse there is no record in invetory)
warehouse 3:0 (beacuse there is no record in invetory)
warehouse 4:0 (beacuse there is no record in invetory)

谢谢，对不起，如果问题已经存在，但我尝试了这些答案，我无法解决我的问题

Answer 1

select a.id, 
       a.name as article_name, 
       w.name as warehouse_name
from article a
left join inventory i on i.article_id = a.id
left join warehouse w on i.warehouse_id = w.id

MySQL LEFT JOIN 3表，怎么做

1 个答案: