SQL多對多排名

Question

我有2個與多對多關係相關的實體

clients，services，clients_has_services。

我需要與各自的客戶的數量檢索所有服務，像這樣：

服務1 20
客服2 10
服務3 5
服務4 0
....

我在進行查詢時遇到問題，此問題只返回一條記錄：

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

您需要按分組劃分：

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