mysql - 连接三个表的Mysql查询

Question

我有三张桌子。

请求- request_id、request_message、requester_id

• 请求者
• requesters_id, requesters_name
• 回应
• response_id、request_id、response_message

我想从 requests 中获取所有字段，requesters_name 从 requester_id在 requests 表中的 requesters 中获取，并从响应表中获取 request_id 的响应数。

请帮帮我。

谢谢

Answer 1

我会从子选择中获取计数，然后将其他两个表与常规连接一起连接

SELECT r.*, rn.requesters_name, 
    (SELECT COUNT(response_id) 
       FROM responses rp WHERE r.request_id=rp.request_id) 
    AS response_count
FROM requests r JOIN requester rn ON r.requesters_id=rn.requesters_id 

Answer 2

SELECT requests.*,requesters.requesters_name,count(1) AS c FROM requests
LEFT JOIN requesters ON requesters.requester_id = request.requester_id
LEFT JOIN responses ON responses.request_id = requests.request_id
GROUP BY requests.request_id