LEFT mysql函数

Question

我如何在规则2中使用mysql的LEFT函数？查询应该如下所示

SELECT LEFT(myfield, N) FROM mytable

Answer 1

您可以像this一样自己实现它。

Answer 2

<?php

use Doctrine\ORM\Query\AST\Functions\FunctionNode;
use Doctrine\ORM\Query\Lexer;

/**
 * JsonbExistence ::= "LEFT('a', 'b')"
 *
 * This will be converted to: "LEFT('a', 'b')"
 *
 */
class LeftFunction extends FunctionNode
{

    public $column = null;
    public $regexp = null;

    public function parse(\Doctrine\ORM\Query\Parser $parser)
    {
        $parser->match(Lexer::T_IDENTIFIER);
        $parser->match(Lexer::T_OPEN_PARENTHESIS);
        $this->column = $parser->ArithmeticPrimary();
        $parser->match(Lexer::T_COMMA);
        $this->regexp = $parser->ArithmeticPrimary();
        $parser->match(Lexer::T_CLOSE_PARENTHESIS);
    }

    public function getSql(\Doctrine\ORM\Query\SqlWalker $sqlWalker)
    {
        return sprintf('LEFT(%s, %s)', $this->column->dispatch($sqlWalker), $this->regexp->dispatch($sqlWalker));
    }
}