MySQL查询联接三个表

Question

I have three Tables.

requests - request_id, request_message, requester_id

• requesters
• requesters_id, requesters_name
• responses
• response_id, request_id, response_message

I want to fetch All the fields from requests , requesters_name from requesters for which requester_id is in requests table and count of responses for request_id from responses table.

please help me out.

Thanks

Answer 1

I'd get the count from a sub-select and just join the other two tables together with a regular join

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