MySql Query optimization : Order by online member - php

Question

I have the following query, which works fine:
SELECT
a.i_am,a.seeking_a,
a.zodiac,
a.my_marital_status,
a.city,a.country,
a.my_age,
a.intrested_in1,
a.intrested_in2,
a.intrested_in3,
a.intrested_in4,
a.intrested_in5,
a.intrested_in6,
a.user_id,
a.picture_type,
a.photo,
a.block_photo,
r.username,
u.title,
u.about_myself
FROM ".TBL_ABOUT_MYSELF." a
INNER JOIN ".TBLREGISTRATION." r ON a.user_id=r.ID
INNER JOIN ".TBLUSERDETAILS." u ON a.user_id=u.user_id
LEFT JOIN ".TBLSTEPS." s ON a.user_id=s.user_id
WHERE 1 $condition $gender_condition
ORDER BY a.user_id
DESC LIMIT $from,10
it takes around 0.5 seconds to fetch results. There are 1,000,000 results in total.
Now if I put join one more table (for user online status:
SELECT
a.i_am,a.seeking_a,
a.zodiac,
a.my_marital_status,
a.city,a.country,
a.my_age,
a.intrested_in1,
a.intrested_in2,
a.intrested_in3,
a.intrested_in4,
a.intrested_in5,
a.intrested_in6,
a.user_id,
a.picture_type,
a.photo,
a.block_photo,
r.username,
u.title,
u.about_myself
FROM ".TBL_ABOUT_MYSELF." a
INNER JOIN ".TBLREGISTRATION." r ON a.user_id=r.ID
INNER JOIN ".TBLUSERDETAILS." u ON a.user_id=u.user_id
LEFT JOIN ".TBLSTEPS." s ON a.user_id=s.user_id
LEFT JOIN ".TBL_USER_ONLINE." ON a.user_id=o.user_id <-- New Line
WHERE 1 $condition $gender_condition
ORDER BY o.user_id DESC, a.user_id DESC LIMIT $from,10 <-- One more order by
and now it takes 12 seconds to fetch results.
How can I optimize this?
mysql Query Explained:
SQL result
Host: localhost
Database: mysite_new
Generation Time: Dec 06, 2012 at 09:09 AM
Generated by: phpMyAdmin 3.2.0.1 / MySQL 5.1.36-community-log
SQL query: EXPLAIN SELECT a.i_am,a.seeking_a,a.zodiac,a.my_marital_status,a.city,a.country,a.my_age,a.intrested_in1,a.intrested_in2,a.intrested_in3,a.intrested_in4,a.intrested_in5,a.intrested_in6,a.user_id,a.picture_type,a.photo,a.block_photo,r.username,u.title, u.about_myself ,o.user_id as online_user_id FROM mysite_about_myself_new a INNER JOIN mysite_user_registration_new r ON a.user_id=r.ID INNER JOIN mysite_user_details_new u ON a.user_id=u.user_id LEFT JOIN mysite_steps_new s ON a.user_id=s.user_id LEFT JOIN mysite_usersonline_new o ON a.user_id=o.user_id WHERE 1 and r.block_by_webmaster='0' and a.approved='1' and s.step1='1' AND a.i_am ='2' AND a.seeking_a = '1' ORDER BY o.user_id DESC LIMIT 0,10;
Rows: 5
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE a ref user_id,i_am i_am 2 const 30011 Using where; Using temporary; Using filesort
1 SIMPLE o ref user_id user_id 4 mysite_new.a.user_id 2 Using index
1 SIMPLE s eq_ref user_id user_id 4 mysite_new.a.user_id 1 Using where
1 SIMPLE u eq_ref user_id user_id 4 mysite_new.s.user_id 1 Using where
1 SIMPLE r eq_ref PRIMARY PRIMARY 4 mysite_new.u.user_id 1 Using where
Second Explain as Asked:
SQL result
Host: localhost
Database: mysite_new
Generation Time: Dec 06, 2012 at 10:02 AM
Generated by: phpMyAdmin 3.2.0.1 / MySQL 5.1.36-community-log
SQL query: EXPLAIN SELECT a.i_am,a.seeking_a,a.zodiac,a.my_marital_status,a.city,a.country,a.my_age,a.intrested_in1,a.intrested_in2,a.intrested_in3,a.intrested_in4,a.intrested_in5,a.intrested_in6,a.user_id,a.picture_type,a.photo,a.block_photo,r.username,u.title, u.about_myself ,o.user_id as online_user_id FROM mysite_about_myself_new a INNER JOIN mysite_user_registration_new r ON a.user_id=r.ID INNER JOIN mysite_user_details_new u ON a.user_id=u.user_id LEFT JOIN mysite_steps_new s ON a.user_id=s.user_id LEFT JOIN mysite_usersonline_new o ON a.user_id=o.user_id WHERE 1 and r.block_by_webmaster='0' and a.approved='1' and s.step1='1' AND a.i_am ='2' AND a.seeking_a = '1' ORDER BY a.user_id DESC LIMIT 0,10;
Rows: 5
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE a index user_id,i_am user_id 4 NULL 38 Using where
1 SIMPLE o ref user_id user_id 4 mysite_new.a.user_id 2 Using index
1 SIMPLE s eq_ref user_id user_id 4 mysite_new.a.user_id 1 Using where
1 SIMPLE u eq_ref user_id user_id 4 mysite_new.s.user_id 1 Using where
1 SIMPLE r eq_ref PRIMARY PRIMARY 4 mysite_new.u.user_id 1 Using where

Answer 1

The problem is most likely in the sorting. Whereas in the first query MySQL could sort using the a.user_id index, in the second query it must perform a filesort of a million records in order to sort over the columns of two tables (and then seek to some point in the resultset to effect the LIMIT clause).
Sorting by o.user_id should be sufficient, since it is either NULL or equal to a.user_id.
Also, if you were instead able to restrict the query with an inequality on o.user_id in a WHERE clause, you would at least not need to seek as far.

Answer 2

why you use order by on two columns
ORDER BY o.user_id DESC, a.user_id DESC
I think o.user_id and a.user_id will be same values for a single user so you can just use one.
o.user_id if you want to include null from tables TBL_USER_ONLINE in order
a.user_id if you want to order only on user ids.
Also use EXPLAIN and create any necessary indexes for joins, where conditions and order by columns

Answer 3

change this new line to
LEFT JOIN ".TBL_USER_ONLINE." o on ON a.user_id=o.user_id
EDIT :
then your problem is with the ORDER BY.
your query takes longs time to ORDER BY two user_id of two tables, try use just one user_id
from one table
EDIT2 :
add this o.user_id also to the SELECT part
like that
SELECT
a.i_am,a.seeking_a,
a.zodiac,
a.my_marital_status,
a.city,a.country,
a.my_age,
a.intrested_in1,
a.intrested_in2,
a.intrested_in3,
a.intrested_in4,
a.intrested_in5,
a.intrested_in6,
a.user_id,
a.picture_type,
a.photo,
a.block_photo,
r.username,
u.title,
u.about_myself
o.user_id <-- New Line