我无法在某些情况下加入 3 个表

Question

我有 3 个表：

省份
城市
住宅

以下是这些表的列：

Provinces:

id , name , status

Cities:

id , province_id , name , status

Residences:

id , province_id , city_id , name , status

我想要所有省份，以及该省拥有的城市数量，当城市至少有 1 个住宅时。

例如：#1省有10个城市，每个城市有10个住宅。

但只有5个城市有city.status = 1并有住宅，只有3个城市有status = 1的住宅。

所以返回的数据应该是：

Province 1 - 3 cities (count cities.id)

省份 1 的所有 3 个城市至少有 1 个状态为 1 的住所

如何查询？

我不会用SQL3

抱歉我的英语不好

谢谢

Answer 1

SELECT
  p.name,
  COUNT(DISTINCT c.id) AS city_count
FROM
  residences   AS r
INNER JOIN
  cities       AS c
    ON c.id = r.city_id
INNER JOIN
  provinces    AS p
    ON p.id = r.province_id
WHERE
      r.status = 1
  AND c.status = 1
  AND p.status = 1
GROUP BY
  p.name

或者...

SELECT
  p.name,
  COUNT(*) AS city_count
FROM
  cities       AS c
INNER JOIN
  provinces    AS p
    ON p.id = c.province_id
WHERE
      c.status = 1
  AND p.status = 1
  AND EXISTS (
    SELECT *
      FROM residences
     WHERE status      = 1
       AND city_id     = c.id
       AND province_id = p.id
  )
GROUP BY
  p.name

我无法在某些情况下加入 3 个表

I can't join 3 tables with some condition

sql

join

count