I have a few queries on a "custom dashboard" of my application, and one of them is taking 10-12 seconds to execute. Using EXPLAIN I can see why it's slow, but I don't know what to do about it. Here is the query:
SELECT person.PersonID,FullName,Furigana,qualdate FROM person
INNER JOIN (
SELECT pq.PersonID,MAX(ContactDate) AS qualdate FROM person pq
INNER JOIN contact cq ON pq.PersonID=cq.PersonID
WHERE cq.ContactTypeID IN (22,26,45) GROUP BY pq.PersonID
) qual ON person.PersonID=qual.PersonID
LEFT OUTER JOIN (
SELECT pe.personID,MAX(ContactDate) AS elimdate FROM person pe
INNER JOIN contact ce ON pe.PersonID=ce.PersonID WHERE ce.ContactTypeID IN (25,31,30,41,23,42,2,33,35,29,12)
GROUP BY pe.PersonID
) elim ON qual.PersonID=elim.PersonID
LEFT OUTER JOIN (
SELECT po.personID FROM person po
INNER JOIN percat pc ON po.PersonID=pc.PersonID WHERE pc.CategoryID=38
) overseas ON qual.PersonID=overseas.PersonID
WHERE (elimdate IS NULL OR qualdate > elimdate)
AND qualdate < CURDATE()-INTERVAL 7 DAY
AND overseas.PersonID IS NULL
ORDER BY qualdate
And here is the EXPLAIN result:
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 5447 Using where; Using temporary; Using filesort
1 PRIMARY <derived3> ALL NULL NULL NULL NULL 5565 Using where
1 PRIMARY <derived4> ALL NULL NULL NULL NULL 9 Using where; Not exists
1 PRIMARY person eq_ref PRIMARY PRIMARY 4 qual.PersonID 1
4 DERIVED pc ref PRIMARY,CategoryID CategoryID 4 8
4 DERIVED po eq_ref PRIMARY PRIMARY 4 kizuna_misa.pc.PersonID 1 Using index
3 DERIVED pe index PRIMARY PRIMARY 4 NULL 5964 Using index
3 DERIVED ce ref PersonID,ContactTypeID PersonID 4 kizuna_misa.pe.PersonID 1 Using where
2 DERIVED pq index PRIMARY PRIMARY 4 NULL 5964 Using index
2 DERIVED cq ref PersonID,ContactTypeID PersonID 4 kizuna_misa.pq.PersonID 1 Using where
I'm sure the first line of the EXPLAIN reveals the problem (comparing with similar queries, it appears that the second line isn't too slow), but I don't know how to fix it. I already have indexes on every column that appears in the joins, but since the tables are <derived2> etc., I guess indexes are irrelevant.
The objective (since it's probably not obvious to someone unfamiliar with my application and schema) is a followup tickler list - if one of the #22/26/45 contacts has occurred but nothing has been done in response (either one of several other contacts or designating by a category assignment that the person is overseas), then the person should appear in the list for followup after waiting a week. Subqueries are easier for me to write and understand than these messy joins, but I can't check the sequence of dates (and subqueries are often slow, also).
MySQL version is 5.0.95 (yeah, I know...). And here is SHOW CREATE TABLE for the three tables involved, even though most of the fields in person are irrelevant:
CREATE TABLE `contact` (
`ContactID` int(11) unsigned NOT NULL auto_increment,
`PersonID` int(11) unsigned NOT NULL default '0',
`ContactTypeID` int(11) unsigned NOT NULL default '0',
`ContactDate` date NOT NULL default '0000-00-00',
`Description` text,
PRIMARY KEY (`ContactID`),
KEY `ContactDate` (`ContactDate`),
KEY `PersonID` (`PersonID`),
KEY `ContactTypeID` (`ContactTypeID`)
) ENGINE=MyISAM AUTO_INCREMENT=16901 DEFAULT CHARSET=utf8
CREATE TABLE `percat` (
`PersonID` int(11) unsigned NOT NULL default '0',
`CategoryID` int(11) unsigned NOT NULL default '0',
PRIMARY KEY (`PersonID`,`CategoryID`),
KEY `CategoryID` (`CategoryID`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8
CREATE TABLE `person` (
`PersonID` int(11) unsigned NOT NULL auto_increment,
`FullName` varchar(100) NOT NULL default '',
`Furigana` varchar(100) NOT NULL default '',
`Sex` enum('','M','F') character set ascii NOT NULL default '',
`HouseholdID` int(11) unsigned NOT NULL default '0',
`Relation` varchar(6) character set ascii NOT NULL default '',
`Title` varchar(6) NOT NULL default '',
`CellPhone` varchar(30) character set ascii NOT NULL default '',
`Email` varchar(70) character set ascii NOT NULL default '',
`Birthdate` date NOT NULL default '0000-00-00',
`Country` varchar(30) NOT NULL default '',
`URL` varchar(150) NOT NULL default '',
`Organization` tinyint(1) NOT NULL default '0',
`Remarks` text NOT NULL,
`Photo` tinyint(1) NOT NULL default '0',
`UpdDate` date NOT NULL default '0000-00-00',
PRIMARY KEY (`PersonID`),
KEY `Furigana` (`Furigana`),
KEY `FullName` (`FullName`),
KEY `Email` (`Email`),
KEY `Organization` (`Organization`,`Furigana`)
) ENGINE=MyISAM AUTO_INCREMENT=6063 DEFAULT CHARSET=utf8
I tried to implement Rick James's suggestion of putting the subselects in the field list (I didn't even know that was possible), like this:
SELECT
p.PersonID,
FullName,
Furigana,
(SELECT MAX(ContactDate) FROM contact cq
WHERE cq.PersonID=p.PersonID
AND cq.ContactTypeID IN (22,26,45))
AS qualdate,
(SELECT MAX(ContactDate) FROM contact ce
WHERE ce.PersonID=p.PersonID
AND ce.ContactTypeID IN (25,31,30,41,23,42,2,33,35,29,12))
AS elimdate
FROM person p
WHERE (elimdate IS NULL OR qualdate > elimdate)
AND qualdate < CURDATE()-INTERVAL 7 DAY
AND NOT EXISTS (SELECT * FROM percat WHERE CategoryID=38 AND percat.PersonID=p.PersonID)
ORDER BY qualdate
But it complains: #1054 - Unknown column 'elimdate' in 'where clause' According to the docs, WHERE clauses are interpreted before field lists, so this approach isn't going to work.
You have an interesting query. I am not sure what the best solution is. Here are two guesses:
Plan A
INDEX(qualdate)
may help. Please provide SHOW CREATE TABLE.
This construct optimizes poorly:
FROM ( SELECT ... )
JOIN ( SELECT ... )
In your case, overseas should probably turned into a JOIN, not a subselect. And the other two should probably be turned into a different flavor of dependent subquery:
SELECT ...,
( SELECT MAX(...) ... ) AS qualdate,
( SELECT MAX(...) ... ) AS elimdate
FROM ...
What version of MySQL are you running?
Plan B
If practical, fold these into the subqueries so that they generate fewer rows, thereby leading to less effort at the outer query. (One per subquery)
elimdate IS NOT NULL
qualdate < CURDATE()-INTERVAL 7 DAY
overseas.PersonID IS NOT NULL
Perhaps the NULL tests apply to LEFT and this suggestion may not apply.