SQL多对多排名

Question

我有2个与多对多关系相关的实体

clients，services，clients_has_services。

我需要与各自的客户的数量检索所有服务，像这样：

服务1 20
客服2 10
服务3 5
服务4 0
....

我在进行查询时遇到问题，此问题只返回一条记录：

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

您需要按分组划分：

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