php 输出pdo的sql

class db{

public $sqlParamIndex = 0; //相当全局变量，不然在匿名函数里无法递增。

function query(){

$params = [“sb”,2];

$sql = “SELECT `value` FROM `sessions` WHERE `id` = ? AND `expire` > ?”;

$index = 0;

$that = $this;

$sqlStr = preg_replace_callback(“|(?)|”, function($match) use($that,$params){ return “‘”.addslashes($params[$that->sqlParamIndex++]).”‘”;},$sql);

echo $sqlStr;

}