Question

I am building a messaging system for a CMS and can not find a way to get the number of unread messages in a message chain.

I need a way to find out if the main message or any of it’s reply messages are unread.

I have a table called “messages” that has the fields:
id, active[1,0], subject, message, datetime, user_from, user_to, reply, viewed, removed

When a message is read I store that users id comma-delimited in the viewed field:
,3,4,12,

Then to find out if it’s viewed I look for the sender’s id like this:

m.viewed LIKE '%,$user_id,%'

I just figure out how to get that logic into this SQL select so that I can see if a parent message should be marked as unread. The following SQL works great and grabs all the messages and the number of replies and orders them by datetime.

SELECT m.*, COUNT(*) AS num_replies, MAX(r.datetime) AS max_datetimeunread_replies
FROM directus_messages AS m
LEFT JOIN directus_messages as r
    ON m.id = r.reply
WHERE m.active = '1' 
AND m.removed NOT LIKE '%,$user_id,%' 
GROUP BY m.id
HAVING m.reply = '0' 
ORDER BY datetime DESC, max_datetime DESC

Any help would be greatly appreciated… I can’t wrap my head around it!

Answer 1

You should check this article: Managing Hierarchical Data in MySQL

–EDIT–UPDATE

OK, you only have 1 level of replies so no need for the above.

Try this:

SELECT m.*
     , COUNT(*) AS num_replies
     , MAX(r.datetime) AS max_datetime
     , (m.viewed LIKE '%,$user_id,%') 
         AS message_viewed    --shows True or False
     , SUM(r.viewed NOT LIKE '%,$user_id,%')
         AS unread_replies    --shows number of unread replies
FROM directus_messages AS m
  LEFT JOIN directus_messages as r
    ON m.id = r.reply
WHERE m.active = '1' 
  AND m.removed NOT LIKE '%,$user_id,%' 
GROUP BY m.id
HAVING m.reply = '0' 
ORDER BY m.datetime DESC
       , max_datetime DESC
;