Last N Rows Of The Query
SELECT expensive query ORDER BY field ASC;
It generates somewhere around 2.9m rows. I want the last 10:
SELECT expensive query ORDER BY field DESC LIMIT 10
But I want them the other way around. Sure, I can do that programatically, but for "application reasons" I want that done in the query, so what I want to do is along the grounds of
SELECT expensive query ORDER BY field LIMIT 10 OFFSET rows()-10
We're using MySQL 4.0. Is there a way to achieve the above without using a temporary table?
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I have tried out some different options: Option 1: (SELECT p.persid FROM person p, perscolor pc, persmaterial pm WHERE p.persid=pc.persid AND (pc.colorid=1 OR pc.colorid=2) AND p.persid=pm.persid AND pm.materialid=2 GROUP BY p.persid HAVING (count(DISTINCT pc.colorid)=2 AND count(DISTINCT pm.materialid)=1)) UNION (SELECT p.persid FROM person p, perscolor pc, persmaterial pm WHERE p.persid=pc.persid AND (pc.colorid=2 OR pc.colorid=3) AND p.persid=pm.persid AND pm.materialid=2 GROUP BY p.persid HAVING (count(DISTINCT pc.colorid)=2 AND count(DISTINCT pm.materialid)=1)) Remarks: *I do not see how to turn a general pseudo query into a query like the one in option 1, except for turning the pseudo query into a sum of products form where the sulms would correspond to the UNIONs. IS there a clever way to obtain such a sum of products form from an arbitrary pseudo query? Option 2: SELECT persid FROM person p WHERE (EXISTS(SELECT * FROM perscolor pc WHERE pc.colorid=1 AND p.persid=pc.persid) OR EXISTS(SELECT * FROM perscolor pc WHERE pc.colorid=3 AND p.persid=pc.persid)) AND EXISTS(SELECT * FROM perscolor pc WHERE pc.colorid=2 AND p.persid=pc.persid) AND EXISTS(SELECT * FROM persmaterial pm WHERE pm.materialid=2 AND p.persid=pm.persid) Remarks: *very easy to get from pseudo query to MySQL query but what about performance? Option 3: SELECT p.persid FROM person p, perscolor pc, persmaterial pm WHERE p.persid=pc.persid AND (pc.colorid=1 OR pc.colorid=2 OR pc.colorid=3) AND p.persid=pm.persid AND pm.materialid=2 GROUP BY p.persid HAVING sum(case when pc.colorid in (Ƈ',Ɖ') then 1 else 0 end) >= 1 AND sum(case when pc.colorid=ƈ' then 1 else 0 end)>=1 AND sum(case when pm.materialid=ƈ' then 1 else 0 end)>=1 Remarks: *this option requires the pseudo query to be turned into a product of sums form; again is their a clever way to obtain such a form; Option 4 SELECT DISTINCT pc1.persid FROM perscolor pc1 INNER JOIN perscolor pc2 ON pc1.persid=pc2.persid AND pc2.colorid=2 INNER JOIN persmaterial pm1 ON pc1.persid=pm1.persid AND pm1.materialid=2 LEFT OUTER JOIN perscolor pc3 ON pc1.persid=pc3.persid AND pc3.colorid=1 LEFT OUTER JOIN perscolor pc4 ON pc1.persid=pc4.persid AND pc4.colorid=3 WHERE COALESCE(pc3.persid,pc4.persid) IS NOT NULL Remarks: *this option requires the pseudo query to be turned into a product of sums form Option 5: SELECT p.persid FROM person p, persmaterial pm,perscolor pc1,perscolor pc2,perscolor pc3 WHERE p.persid=pm.persid AND p.persid=pc1.persid AND p.persid=pc2.persid AND p.persid=pc3.persid AND (pc1.colorid=1 OR pc2.colorid=3) AND pc3.colorid=2 AND pm.materialid=2 GROUP BY p.persid Remarks: *very easy to get from pseudo query to MySQL query but what about performance? -- phpMyAdmin SQL Dump -- version 2.6.1 -- http://www.phpmyadmin.net -- -- Host: localhost -- Generation Time: Oct 19, 2006 at 01:13 PM -- Server version: 4.1.9 -- PHP Version: 4.3.10 -- -- Database: `aston` -- -- -------------------------------------------------------- -- -- Table structure for table `color` -- CREATE TABLE `color` ( `colorid` int(11) NOT NULL auto_increment, `color` varchar(30) NOT NULL default '', PRIMARY KEY (`colorid`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=5 ; -- -- Dumping data for table `color` -- INSERT INTO `color` VALUES (1, 'red'); INSERT INTO `color` VALUES (2, 'green'); INSERT INTO `color` VALUES (3, 'blue'); INSERT INTO `color` VALUES (4, 'yellow'); -- -------------------------------------------------------- -- -- Table structure for table `material` -- CREATE TABLE `material` ( `materialid` int(11) NOT NULL auto_increment, `material` varchar(30) NOT NULL default '', PRIMARY KEY (`materialid`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ; -- -- Dumping data for table `material` -- INSERT INTO `material` VALUES (1, 'wood'); INSERT INTO `material` VALUES (2, 'iron'); -- -------------------------------------------------------- -- -- Table structure for table `perscolor` -- CREATE TABLE `perscolor` ( `perscolorid` int(11) NOT NULL auto_increment, `persid` int(11) NOT NULL default Ɔ', `colorid` int(11) NOT NULL default Ɔ', PRIMARY KEY (`perscolorid`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=7 ; -- -- Dumping data for table `perscolor` -- INSERT INTO `perscolor` VALUES (1, 1, 1); INSERT INTO `perscolor` VALUES (2, 1, 2); INSERT INTO `perscolor` VALUES (3, 2, 1); INSERT INTO `perscolor` VALUES (5, 3, 3); INSERT INTO `perscolor` VALUES (6, 3, 2); -- -------------------------------------------------------- -- -- Table structure for table `persmaterial` -- CREATE TABLE `persmaterial` ( `persmatid` int(11) NOT NULL auto_increment, `persid` int(11) NOT NULL default Ɔ', `materialid` int(11) NOT NULL default Ɔ', PRIMARY KEY (`persmatid`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=6 ; -- -- Dumping data for table `persmaterial` -- INSERT INTO `persmaterial` VALUES (1, 1, 1); INSERT INTO `persmaterial` VALUES (2, 1, 2); INSERT INTO `persmaterial` VALUES (3, 2, 1); INSERT INTO `persmaterial` VALUES (5, 3, 2); -- -------------------------------------------------------- -- -- Table structure for table `person` -- CREATE TABLE `person` ( `persid` int(11) NOT NULL auto_increment, `name` varchar(30) NOT NULL default '', PRIMARY KEY (`persid`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=4 ; -- -- Dumping data for table `person` -- INSERT INTO `person` VALUES (1, 'john'); INSERT INTO `person` VALUES (2, 'emily'); INSERT INTO `person` VALUES (3, 'liz');
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