Question

hello i have this SQL witch is supposed to give me the max(messages.message_id)
so i have the record where the first message_id is 7 and the last message_id is 10, but instead of giving me 10 it gives me 7… it is completely ignoring the MAX(messages.message_id) and giving me the first message_id… any suggestions on how to fix this?

SELECT
  profile.first_name,
  profile.last_name,
  conversations.conversation_hash,
  conversations.person_a,
  conversations.person_b,
  messages.conversation_hash,
  MAX(messages.message_id),
  messages.message,
  messages.subject,
  messages.date
FROM conversations
  INNER JOIN messages
    ON conversations.conversation_hash = messages.conversation_hash
  INNER JOIN profile
    ON profile.id = conversations.person_b
WHERE conversations.person_a = '$id'
GROUP BY messages.conversation_hash
ORDER BY messages.message_id DESC

tables:
conversations:

conversation_id | conversation_hash | person_a | person_b |

messages:

conversation_hash | from_id | to_id | message_id | subject | message | date

Answer 1

You can separately get the latest message_id from table messages inside a subquery and the result of it is then join back against the tables provided that it match on two conditions: conversation_hash and message_id.

Full Query:

SELECT  profile.first_name,
        profile.last_name,
        conversations.conversation_hash,
        conversations.person_a,
        conversations.person_b,
        messages.*
FROM    conversations
        INNER JOIN messages
            ON conversations.conversation_hash = messages.conversation_hash
        INNER JOIN  
        (
            SELECT  conversation_hash, MAX(message_id) max_ID
            FROM    messages
            GROUP   BY conversation_hash
        ) c ON messages.conversation_hash = c.conversation_hash AND
                messages.message_id = c.max_ID
        INNER JOIN profile
            ON profile.id=conversations.person_b
WHERE   conversations.person_a='$id'
ORDER   BY messages.message_id DESC