Question

我有两个与多对多关系相关的实体

客户，服务，clients_has_services。

我需要检索具有各自客户数量的所有服务，如下所示：

服务1 20
Service2 10
Service3 5
Service4 0
....

我在查询时遇到问题，这只会返回一条记录：

SELECT
    services.id as id,
    services.name as name,
    COUNT(clients_has_services.services_id) as ranking
FROM services
LEFT JOIN clients_has_services ON services.id = clients_has_services.services_id

Answer 1

你需要一个group by子句：

SELECT
    services.id as id,
    services.name as name,
    COUNT(clients_has_services.services_id) as ranking
FROM services
LEFT JOIN clients_has_services ON services.id = clients_has_services.services_id
GROUP BY
    services.id,
    services.name

SQL多对多排名

1 个答案: