Question

我有两个桌子

https://stackoverflow.com/questions/38969419/ios-how-can-enable-or-disable-rotate-on-each-uiviewcontroller

我像这样加入两者：

Table name: place
Columns: placeid, name
Data: 1, My Favourite Donut Place

Table name: category
Columns: categoryid, name, placeid
Data: 1, Donuts, 1
      2, Coffee, 1
      3, Hot Chocolate, 1

会得到这样的结果：

 select p.name as place, c.name as category from place p join category c on p.placeid=c.placeid

现在，我想搜索提供咖啡的地方：

place                     category
My favourite donut place  Donuts
My favourite donut place  Coffee
My favourite donut place  Hot Chocolate

结果如下：

select p.name as place, c.name as category from place p join category c on p.placeid=c.placeid where c.name = 'Coffee'

但是我仍然想显示“我最喜欢的咖啡甜甜圈店”的所有不同类别，即“甜甜圈”和“热巧克力”。

要实现这一目标的最佳方法是什么？

Answer 1

您只需对类别进行第二个位置连接即可获得所有类别，虽然在这种情况下连接顺序并不重要，但我发现这种顺序更清楚了。

SELECT p.name AS place, placeCategories .name AS category 
FROM category AS filterCategory 
INNER JOIN place AS p ON filterCategory.placeid=p.placeid 
INNER JOIN category AS placeCategories ON p.placeid=placeCategories.placeid 
WHERE filterCategory.name = 'Coffee'

MySQL的加入，扩展了结果

1 个答案: