Help me optimize this MySql query - mysql

Question

I have a MySql query that take a very long time to run (about 7 seconds). The problem seems to be with the OR in this part of the query: "(tblprivateitem.userid=?userid OR tblprivateitem.userid=1)". If I skip the "OR tblprivateitem.userid=1" part it takes only 0.01 seconds. As I need that part I need to find a way to optimize this query. Any ideas?
QUERY:
SELECT
tbladdeditem.addeditemid,
tblprivateitem.iitemid,
tblprivateitem.itemid
FROM tbladdeditem
INNER JOIN tblprivateitem
ON tblprivateitem.itemid=tbladdeditem.itemid
AND (tblprivateitem.userid=?userid OR tblprivateitem.userid=1)
WHERE tbladdeditem.userid=?userid
EXPLAIN:
id select_type table type possible_keys key key_len ref rows extra
1 SIMPLE tbladdeditem ref userid userid 4 const 293 Using where
1 SIMPLE tblprivateitem ref userid,itemid itemid 4 tbladdeditem.itemid 2 Using where
TABLES:
tbladdeditem contains 1 100 000 rows:
CREATE TABLE `tbladdeditem` (
`addeditemid` int(11) NOT NULL auto_increment,
`itemid` int(11) default NULL,
`userid` mediumint(9) default NULL,
PRIMARY KEY (`addeditemid`),
KEY `userid` (`userid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
tblprivateitem contains 2 700 000 rows:
CREATE TABLE `tblprivateitem` (
`privateitemid` int(11) NOT NULL auto_increment,
`userid` mediumint(9) default '1',
`itemid` int(10) NOT NULL,
`iitemid` mediumint(9) default NULL,
PRIMARY KEY (`privateitemid`),
KEY `userid` (`userid`),
KEY `itemid` (`itemid`) //Changed this index to only use itemid instead
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Answer 1

UPDATE
I made my queries and schema match your original question exactly, multi-column key and all. The only possible difference is that I populated each table with two million entries. My query (your query) runs in 0.15 seconds.
delimiter $$
set #userid = 6
$$
SELECT
tbladdeditem.addeditemid, tblprivateitem.iitemid, tblprivateitem.itemid
FROM tbladdeditem
INNER JOIN tblprivateitem
ON tblprivateitem.itemid=tbladdeditem.itemid
AND (tblprivateitem.userid=#userid or tblprivateitem.userid = 1)
WHERE tbladdeditem.userid=#userid
I have the same explain that you do, and with my data, my query return over a thousand matches without any issue at all. Being completely at a loss, as you really shouldn't be having these issues -- is it possible you are running a very limiting version of MySQL? Are you running 64-bit? Plenty of memory?
I had made the assumption that your query wasn't performing well, and when mine was, assumed I had fixed you problem. So now I eat crow. I'll post some of the avenues I went down. But I'm telling you, your query the way you posted it originally works just fine. I can only imagine your MySQL thrashing to the hard drive or something. Sorry I couldn't be more help.
PREVIOUS RESPONSE (Which is also an update)
I broke down and recreated your problem in my own database. After trying independent indexes on userid and on itemid I was unable to get the query below a few seconds, so I set up very specific multi-column keys as directed by the query. Notice on tbladdeditem the multi-column query begins with itemid while on the tblprivateitem the columns are reversed:
Here is the schema I used:
CREATE TABLE `tbladdeditem` (
`addeditemid` int(11) NOT NULL AUTO_INCREMENT,
`itemid` int(11) NOT NULL,
`userid` mediumint(9) NOT NULL,
PRIMARY KEY (`addeditemid`),
KEY `userid` (`userid`),
KEY `i_and_u` (`itemid`,`userid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `tblprivateitem` (
`privateitemid` int(11) NOT NULL AUTO_INCREMENT,
`userid` mediumint(9) NOT NULL DEFAULT '1',
`itemid` int(10) NOT NULL,
`iitemid` mediumint(9) NOT NULL,
PRIMARY KEY (`privateitemid`),
KEY `userid` (`userid`),
KEY `itemid` (`itemid`),
KEY `u_and_i` (`userid`,`itemid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
I filled each table with 2 million entries of random data. I made some assumptions:
userid varies from 1 to 2000
itemid varies between 1 and 10000
This gives each user about a thousand entries in each table.
Here are two versions of the query (I'm using workbench for my editor):
Version 1 - do all the filtering on the join.
Result: 0.016 seconds to return 1297 rows
delimiter $$
set #userid = 3
$$
SELECT
a.addeditemid,
p.iitemid,
p.itemid
FROM tblprivateitem as p
INNER JOIN tbladdeditem as a
ON (p.userid in (1, #userid))
AND p.itemid = a.itemid
AND a.userid = #userid
$$
Here's the explain:
EXPLAIN:
id select_type table type key ref rows extra
1 SIMPLE p range u_and_i 2150 Using where; Using index
1 SIMPLE a ref i_and_u 1 Using where; Using index
Version 2 - filter up front
Result: 0.015 seconds to return 1297 rows
delimiter $$
set #userid = 3
$$
SELECT
a.addeditemid,
p.iitemid,
p.itemid
from
(select userid, itemid, iitemid from tblprivateitem
where userid in (1, #userid)) as p
join tbladdeditem as a on p.userid = a.userid and a.itemid = p.itemid;
where a.userid = #userid
$$
Here's the explain:
id select_type table type key ref rows extra
1 PRIMARY <derived2> ALL null null 2152
1 PRIMARY a ref i_and_u p.itemid,const 1 Using where; Using index
2 DERIVED p1 range u_and_i 2150 Using where

Answer 2

Since you have the predicate condition tbladdeditem.userid=?userid in the where clause I don't think you need it in the join condition.. Try removing it from the join condition and (If you are using the Or to handle the case where the parameter is null, then use Coalesce instead of OR) if not leave it as an Or
-- If Or is to provide default for when (?userid is null...
SELECT a.addeditemid, p.iitemid, p.itemid
FROM tbladdeditem a
JOIN tblprivateitem p
ON p.itemid=a.itemid
WHERE a.userid=?userid
AND p.userid=Coalesce(?userid, 1)
-- if not then
SELECT a.addeditemid, p.iitemid, p.itemid
FROM tbladdeditem a
JOIN tblprivateitem p
ON p.itemid=a.itemid
WHERE a.userid=?userid
AND (p.userid=?userid Or p.userid = 1)
Second, if there is not an index on the userId column in these two tables, consider adding one.
Finally, if these all fail, try converting to two separate queries and unioning them together:
Select a.addeditemid, p.iitemid, p.itemid
From tbladdeditem a
Join tblprivateitem p
On p.itemid=a.itemid
And p.userId = a.Userid
Where p.userid=?userid
Union
Select a.addeditemid, p.iitemid, p.itemid
From tbladdeditem a
Join tblprivateitem p
On p.itemid=a.itemid
And p.userId = a.Userid
Where p.userid = 1

Answer 3

I would try this instead, on your original JOIN you have an OR associated with a parameter, move that to your WHERE clause.
SELECT
tbladdeditem.addeditemid,
tblprivateitem.iitemid,
tblprivateitem.itemid
FROM tbladdeditem
INNER JOIN tblprivateitem
ON tblprivateitem.itemid=tbladdeditem.itemid
WHERE tbladdeditem.userid=?userid
AND (tblprivateitem.userid=?userid OR tblprivateitem.userid=1)