mysql - 3张表之间的特殊连接

Question

我创建了 3 个 mysql 表:

表“城市”:包含城市

i.e   |  name  |
      +========+
      | Athens |
      +--------+
      | Rome   |
      +--------+
      | Paris  |
      +--------+

表“类别”:包含类别

i.e   |    name    |
      +============+
      | category_1 |
      +------------+
      | category_2 |
      +------------+

表“shops”:包含商店

i.e   |  name  |  category_name  |  city_name  |
      +========+=================+=============+
      | shop_1 |   category_2    |    Rome     |
      +--------+-----------------+-------------|
      | shop_2 |   category_2    |    Rome     |
      +--------+-----------------+-------------+
      | shop_3 |   category_1    |    Paris    |
      +--------+-----------------+-------------+

我正在尝试创建一个查询，该查询将允许我创建以下 html 数组(显示每个城市按类别分组的商店数量):

|        ||   category_1   |  category_2 |
+========++================+=============+
| Athens ||        0       |      0      |
+--------++----------------+-------------|
| Rome   ||        0       |      2      |
+--------++----------------+-------------+
| Paris  ||        1       |      0      |
+--------++----------------+-------------+

预先感谢您，扬尼斯

Answer 1

试试这个

select c.name,
sum(case when s.category_name='category_1' then 1 else 0 end) as categoty_1,
sum(case when s.category_name='category_2' then 1 else 0 end) as categoty_2
from city as c left join shops as s on c.name=s,city_name
group by c.name