Support for STRAIGHT_JOIN in Doctrine. This does not work (yet) because not having a clean way to implement it. But making these changes in Doctrine directly will work.

MysqlJoin.php

<?php
/**
 * DoctrineExtensions Vendor Specific DQL Query Features
 *
 * LICENSE
 *
 * This source file is subject to the new BSD license that is bundled
 * with this package in the file LICENSE.txt.
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to kontakt@beberlei.de so I can send you a copy immediately.
 */

namespace DoctrineExtensions\Query\AST;

use Doctrine\ORM\Query\AST\Join;

/**
 * Join ::= [["LEFT" ["OUTER"] | "INNER"] "JOIN" | "STRAIGHT_JOIN"] JoinAssociationPathExpression
 *          ["AS"] AliasIdentificationVariable [("ON" | "WITH") ConditionalExpression]
 *
 * @link    www.doctrine-project.org
 * @since   2.0
 * @author  Guilherme Blanco <guilhermeblanco@hotmail.com>
 * @author  Jonathan Wage <jonwage@gmail.com>
 * @author  Roman Borschel <roman@code-factory.org>
 */
class MysqlJoin extends Join
{
    const JOIN_TYPE_STRAIGHT  = 4;
}

MysqlLexer.php

<?php
/**
 * DoctrineExtensions Vendor Specific DQL Query Features
 *
 * LICENSE
 *
 * This source file is subject to the new BSD license that is bundled
 * with this package in the file LICENSE.txt.
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to kontakt@beberlei.de so I can send you a copy immediately.
 */

namespace DoctrineExtensions\Query;

use Doctrine\ORM\Query\Lexer;

/**
 * Scans a DQL query for tokens.
 *
 * @author Guilherme Blanco <guilhermeblanco@hotmail.com>
 * @author Janne Vanhala <jpvanhal@cc.hut.fi>
 * @author Roman Borschel <roman@code-factory.org>
 * @since 2.0
 */
class MysqlLexer extends Lexer
{
    const T_STRAIGHT_JOIN       = 158;
}

MysqlParser.php

<?php
/**
 * DoctrineExtensions Vendor Specific DQL Query Features
 *
 * LICENSE
 *
 * This source file is subject to the new BSD license that is bundled
 * with this package in the file LICENSE.txt.
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to kontakt@beberlei.de so I can send you a copy immediately.
 */

namespace DoctrineExtensions\Query;

use Doctrine\ORM\Query\Parser;

/**
 * An LL(*) recursive-descent parser for the context-free grammar of the Doctrine Query Language.
 * Parses a DQL query, reports any errors in it, and generates an AST.
 *
 * @since   2.0
 * @author  Guilherme Blanco <guilhermeblanco@hotmail.com>
 * @author  Jonathan Wage <jonwage@gmail.com>
 * @author  Roman Borschel <roman@code-factory.org>
 * @author  Janne Vanhala <jpvanhal@cc.hut.fi>
 * @author  Fabio B. Silva <fabio.bat.silva@gmail.com>
 */
class MysqlParser extends Parser
{
    /**
     * IdentificationVariableDeclaration ::= RangeVariableDeclaration [IndexBy] {Join}*
     *
     * @return \Doctrine\ORM\Query\AST\IdentificationVariableDeclaration
     */
    public function IdentificationVariableDeclaration()
    {
        $rangeVariableDeclaration = $this->RangeVariableDeclaration();

        $rangeVariableDeclaration->isRoot = true;

        $indexBy = $this->lexer->isNextToken(Lexer::T_INDEX) ? $this->IndexBy() : null;
        $joins   = array();

        while (
            $this->lexer->isNextToken(Lexer::T_LEFT) ||
            $this->lexer->isNextToken(Lexer::T_INNER) ||
            $this->lexer->isNextToken(Lexer::T_JOIN) ||
            $this->lexer->isNextToken(Lexer::T_STRAIGHT_JOIN)
        ) {
            $joins[] = $this->Join();
        }

        return new AST\IdentificationVariableDeclaration(
            $rangeVariableDeclaration, $indexBy, $joins
        );
    }

    /**
     * Join ::= [["LEFT" ["OUTER"] | "INNER"] "JOIN" | "STRAIGHT_JOIN"]
     *          (JoinAssociationDeclaration | RangeVariableDeclaration)
     *          ["WITH" ConditionalExpression]
     *
     * @return \Doctrine\ORM\Query\AST\Join
     */
    public function Join()
    {
        // Check Join type
        $joinType = AST\Join::JOIN_TYPE_INNER;

        switch (true) {
            case ($this->lexer->isNextToken(Lexer::T_LEFT)):
                $this->match(Lexer::T_LEFT);

                $joinType = AST\Join::JOIN_TYPE_LEFT;

                // Possible LEFT OUTER join
                if ($this->lexer->isNextToken(Lexer::T_OUTER)) {
                    $this->match(Lexer::T_OUTER);

                    $joinType = AST\Join::JOIN_TYPE_LEFTOUTER;
                }
                $this->match(Lexer::T_JOIN);
                break;

            case ($this->lexer->isNextToken(Lexer::T_INNER)):
                $this->match(Lexer::T_INNER);
                $this->match(Lexer::T_JOIN);
                break;

            case ($this->lexer->isNextToken(Lexer::T_STRAIGHT_JOIN)):
                $joinType = AST\Join::JOIN_TYPE_STRAIGHT;
                $this->match(Lexer::T_STRAIGHT_JOIN);
                break;

            default:
                // Do nothing
        }

        $next            = $this->lexer->glimpse();
        $joinDeclaration = ($next['type'] === Lexer::T_DOT) ? $this->JoinAssociationDeclaration() : $this->RangeVariableDeclaration();
        $adhocConditions = $this->lexer->isNextToken(Lexer::T_WITH);
        $join            = new AST\Join($joinType, $joinDeclaration);

        // Describe non-root join declaration
        if ($joinDeclaration instanceof AST\RangeVariableDeclaration) {
            $joinDeclaration->isRoot = false;

            $adhocConditions = true;
        }

        // Check for ad-hoc Join conditions
        if ($adhocConditions) {
            $this->match(Lexer::T_WITH);

            $join->conditionalExpression = $this->ConditionalExpression();
        }

        return $join;
    }
}

MysqlWalker.php

<?php
/**
 * DoctrineExtensions Vendor Specific DQL Query Features
 *
 * LICENSE
 *
 * This source file is subject to the new BSD license that is bundled
 * with this package in the file LICENSE.txt.
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to kontakt@beberlei.de so I can send you a copy immediately.
 */

namespace DoctrineExtensions\Query;

use Doctrine\ORM\Query\SqlWalker;

class MysqlWalker extends SqlWalker
{
    /**
     * Walks down a SelectClause AST node, thereby generating the appropriate SQL.
     *
     * @param $selectClause
     * @return string The SQL.
     */
    public function walkSelectClause($selectClause)
    {
        $sql = parent::walkSelectClause($selectClause);

        if ($this->getQuery()->getHint('mysqlWalker.sqlNoCache') === true) {
            if ($selectClause->isDistinct) {
                $sql = str_replace('SELECT DISTINCT', 'SELECT DISTINCT SQL_NO_CACHE', $sql);
            } else {
                $sql = str_replace('SELECT', 'SELECT SQL_NO_CACHE', $sql);
            }
        }

        return $sql;
    }

    /**
     * Walks down a Join AST node and creates the corresponding SQL.
     *
     * @param AST\Join $join
     *
     * @return string The SQL.
     */
    public function walkJoin($join)
    {
        $joinType        = $join->joinType;
        $joinDeclaration = $join->joinAssociationDeclaration;

        if ($joinType == AST\Join::JOIN_TYPE_LEFT || $joinType == AST\Join::JOIN_TYPE_LEFTOUTER) {
            $sql = ' LEFT JOIN ';
        } elseif ($joinType == AST\Join::JOIN_TYPE_STRAIGHT) {
            $sql = ' STRAIGHT_JOIN ';
        } else {
            $sql = ' INNER JOIN ';
        }

        switch (true) {
            case ($joinDeclaration instanceof \Doctrine\ORM\Query\AST\RangeVariableDeclaration):
                $class      = $this->em->getClassMetadata($joinDeclaration->abstractSchemaName);
                $dqlAlias   = $joinDeclaration->aliasIdentificationVariable;
                $tableAlias = $this->getSQLTableAlias($class->table['name'], $dqlAlias);
                $condition = '(' . $this->walkConditionalExpression($join->conditionalExpression) . ')';
                $condExprConjunction = ($class->isInheritanceTypeJoined() && $joinType != AST\Join::JOIN_TYPE_LEFT && $joinType != AST\Join::JOIN_TYPE_LEFTOUTER)
                    ? ' AND '
                    : ' ON ';

                $sql .= $this->walkRangeVariableDeclaration($joinDeclaration);

                $conditions = array($condition);

                // Apply remaining inheritance restrictions
                $discrSql = $this->_generateDiscriminatorColumnConditionSQL(array($dqlAlias));

                if ($discrSql) {
                    $conditions[] = $discrSql;
                }

                // Apply the filters
                $filterExpr = $this->generateFilterConditionSQL($class, $tableAlias);

                if ($filterExpr) {
                    $conditions[] = $filterExpr;
                }

                $sql .= $condExprConjunction . implode(' AND ', $conditions);
                break;

            case ($joinDeclaration instanceof \Doctrine\ORM\Query\AST\JoinAssociationDeclaration):
                $sql .= $this->walkJoinAssociationDeclaration($joinDeclaration, $joinType, $join->conditionalExpression);
                break;
        }

        return $sql;
    }
}