MySQL查詢聯接三個表

Question

我有三個桌子。

請求 -request_id，request_message，requester_id

• 請求者
• requesters_id，requesters_name
• 回應
• response_id，request_id，response_message

我想從requests中獲取所有字段 ， 從requesters中獲取requester_id的請求者的requesters_name，並從響應表中獲取request_id的響應計數 。

請幫幫我。

謝謝

Answer 1

我將從子選擇中獲取計數，然后將其他兩個表與常規聯接一起聯接

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