Optimize SQL query (Facebook-like application) - mysql

Question

My application is similar to Facebook, and I'm trying to optimize the query that get user records. The user records are that he as src ou dst. The src is in usermuralentry directly, the dst list are in usermuralentry_user.
So, a entry can have one src and many dst.
I have those tables:
mysql> desc usermuralentry ;
+-----------------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------------+------------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| user_src_id | int(11) | NO | MUL | NULL | |
| private | tinyint(1) | NO | | NULL | |
| content | longtext | NO | | NULL | |
| date | datetime | NO | | NULL | |
| last_update | datetime | NO | | NULL | |
+-----------------+------------------+------+-----+---------+----------------+
10 rows in set (0.10 sec)
mysql> desc usermuralentry_user ;
+-------------------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------------+---------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| usermuralentry_id | int(11) | NO | MUL | NULL | |
| userinfo_id | int(11) | NO | MUL | NULL | |
+-------------------+---------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
And the following query to retrieve information from two users.
mysql> explain
SELECT *
FROM usermuralentry AS a
, usermuralentry_user AS b
WHERE a.user_src_id IN ( 1, 2 )
OR
(
a.id = b.usermuralentry_id
AND b.userinfo_id IN ( 1, 2 )
);
+----+-------------+-------+------+-------------------------------------------------------------------------------------------+------+---------+------+---------+------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+-------------------------------------------------------------------------------------------+------+---------+------+---------+------------------------------------------------+
| 1 | SIMPLE | b | ALL | usermuralentry_id,usermuralentry_user_bcd7114e,usermuralentry_user_6b192ca7 | NULL | NULL | NULL | 147188 | |
| 1 | SIMPLE | a | ALL | PRIMARY | NULL | NULL | NULL | 1371289 | Range checked for each record (index map: 0x1) |
+----+-------------+-------+------+-------------------------------------------------------------------------------------------+------+---------+------+---------+------------------------------------------------+
2 rows in set (0.00 sec)
but it is taking A LOT of time...
Some tips to optimize? Can the table schema be better in my application?

Answer 1

Use this query
SELECT *
FROM usermuralentry AS a
left join usermuralentry_user AS b
on b.usermuralentry_id = a.id
WHERE a.user_src_id IN(1, 2)
OR (a.id = b.usermuralentry_id
AND b.userinfo_id IN(1, 2));
And for some tips here are
You are using two tables in from clause which is a cartision product and will take a lot of time as well as undesired results. Always use joins in this situation.

Answer 2

I think your join isn't properly formed, and you need to change the query to use UNION. The OR condition in the where clause is killing performance as well:
SELECT *
FROM usermuralentry AS a
JOIN usermuralentry_user AS b ON a.id = b.usermuralentry_id /* use explicit JOIN! */
WHERE a.user_src_id IN (1 , 2)
UNION
SELECT *
FROM usermuralentry AS a
JOIN usermuralentry_user AS b ON a.id = b.usermuralentry_id
WHERE b.usermuralentry_id IN ( 1, 2 )
You also need an index: ALTER TABLE usermuralentry_user ADD INDEX (usermuralentry_id)