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MySQL RAND() function in Doctrine2 DQL
<?php
$config = new \Doctrine\ORM\Configuration();
/** OTHER STUFF */
$config->addCustomNumericFunction('RAND', 'My\Custom\Doctrine2\Function\Rand');
/** CONTINUES */
<?php
namespace My\Custom\Doctrine2\Function;
/**
* RandFunction ::= "RAND" "(" ")"
*/
class Rand extends FunctionNode
{
public function parse(\Doctrine\ORM\Query\Parser $parser)
{
$parser->match(Lexer::T_IDENTIFIER);
$parser->match(Lexer::T_OPEN_PARENTHESIS);
$parser->match(Lexer::T_CLOSE_PARENTHESIS);
}
public function getSql(\Doctrine\ORM\Query\SqlWalker $sqlWalker)
{
return 'RAND()';
}
}
@Ocramius

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Ocramius commented Apr 14, 2011

@lmlopez

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lmlopez commented Jun 26, 2013

I am using this code in my project, but I have this error, any idea?

Message: [Syntax Error] line 0, col 130: Error: Expected end of string, got '('

@wardpeet

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wardpeet commented Jul 10, 2013

@lmlopez it is working but you need to change something in your querybuilder or dql

$q = $this->createQueryBuilder('e')
    ->addSelect('RAND() as HIDDEN rand')
    ->orderBy('rand');
@Abhoryo

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Abhoryo commented Jul 24, 2013

Warning @wardpeet: The doc says : "You cannot use a column with RAND() values in an ORDER BY clause, because ORDER BY would evaluate the column multiple times. "

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Abhoryo commented Jul 24, 2013

@lmlopez I have the same error.

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Ocramius commented Feb 28, 2014

Sorting by rand is a BAD idea. Don't do it!

@jeroensen

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jeroensen commented Mar 25, 2014

Why is sorting by RAND() a bad idea?!? When you need some random data from the database this is actually a very simple and fast solution (since ordering by rand doesn't force any index to be created by the database (btree indexes and the like that is)). So it's actually a very cheap solution in terms of processor cycles.

If you would implement this in code it would not only take more time (to implement) but also more processor cycles.

Care to comment on that?

@gabrielthakid

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gabrielthakid commented Apr 16, 2014

I have the same problem
Message: [Syntax Error] line 0, col 130: Error: Expected end of string, got '('

Has someone fixed this yet?

@nocomment17

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nocomment17 commented May 30, 2014

I have the same problem
Message: [Syntax Error] line 0, col 226: Error: Expected end of string, got '('

Has someone fixed this yet?

http://www.doctrine-project.org/blog/doctrine2-custom-dql-udfs => 404

@gusdecool

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gusdecool commented Jan 16, 2015

This code messed up when using with JOIN query.

@dvapelnik

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dvapelnik commented Oct 22, 2015

Sorting by rand is a BAD idea. Don't do it!

@Ocramius why?

@BenMorel

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BenMorel commented Feb 16, 2016

@jeroensen @dvapelnik IIRC, sorting by RAND() forces a scan of all matching records, as RAND() is just a numerical function that returns a random number. If there is a small number of matching records, it should be alright. But if you have millions of matching records and attempt something like ORDER BY RAND() LIMIT 10, you might be in trouble, as the database will have to scan all these rows, remember all of them along with the number returned by RAND() for each of them, then extract the few ones with the lowest number (someone correct me if I'm wrong on the details). This is very resource intensive.

There are more efficient ways to select randomly. See for example:
http://jan.kneschke.de/projects/mysql/order-by-rand/

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