Mysql Php combining 3 tables - php

Question

basically in this web app i have an event module where user can create, edit and delete an event also can upload photo for that event. Other users either can involve in particular event by selecting I'm in button or just mentioning the event Sound's Cool.
For now there is 3 tables event_photo (user upload pic will be saved here), event_in and event_cool, now i need an event activity feed, for that i need to combine all 3 tables by grouping them as photo, in and cool. So i need suggestion whether to create a single table to list these activity or should i combine all the results in php. Previously i combine all 2 results in single table but now i want to try something different. There are the table structure.
event_photo table
id photo_url business_id event_id user_id caption added_date
1 1111 12 2 3 test1 20130209t1
2 1122 13 3 4 test2 20130209t4
3 1133 14 2 3 test3 20130209t2
event_in table
id event_id user_id date_created
1 2 3 20130209t3
event_cool
id event_id user_id date_created
1 2 4 20130209t5
2 3 3 20130209t6
Now the feed will be like this, based on date_created desc t6 -> t1
User_3 says cool for Event_3
User_4 says cool for Event_2
User_4 added photo for Event_3
User_3 added photo for Event_2
User_3 attending Event_2
User_3 added photo for Event_2
User_3 added photo for Event_2
Now how the table should be design, i hope this is important questions as this can resolve many problems regarding activity feed.Thanks

Answer 1

An option would be to have your three tables and query them with something similar to:
SELECT *
FROM
( SELECT user_id,
event_id,
date_added as date_created,
'photo' as type
FROM event_photo
UNION
SELECT user_id,
event_id,
date_created,
'event_in' as type
FROM event_in
UNION
SELECT user_id,
event_id,
date_created,
'event_cool' as type
FROM event_cool
) s
ORDER BY date_created
To simplify your code, you could create a view:
CREATE OR REPLACE VIEW v_ordered_actions AS
SELECT *
FROM
( SELECT user_id,
event_id,
date_added as date_created,
'photo' as type
FROM event_photo
UNION
SELECT user_id,
event_id,
date_created,
'event_in' as type
FROM event_in
UNION
SELECT user_id,
event_id,
date_created,
'event_cool' as type
FROM event_cool
) s
ORDER BY date_created;

Answer 2

You can use UNION of course: http://dev.mysql.com/doc/refman/5.1/en/union.html However, this is quite slow. Maybe better to create next table, like activity log, where to store just:
entity_type (in/cool/photo)
entity_id (id of row in target table)
event_id
user_id
date
And select via this. When you have selected that, collect all IDs seperatelly for each target table, and get necessary info from that tables (if necessary) returned as indexed array. Foreach activity feed and assign correct data you need for it.
Hope this can help you.