學說LEFT mysql函數

Question

我該如何使用2號教條的LEFT函數？查詢應該是這個樣子

SELECT LEFT(myfield, N) FROM mytable 

Answer 1

你可以自己實現它像this。

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)); 
    } 
}