zend framework2 dbadapter查询语句不起作用，当使用“where in”时

I post my code here, I was debug in z-ray and check the rawSQL in mysql-command. If I run the second time's rawSQL, I can get tow row (the 686 and 687). But it doesn't work in ZF2.

$sql =  "select * from kd_oa_userinfo where user_id in (:user_id)";
$statement  = $this->adapter->createStatement($sql);
//first time,i set the $sqlArg = array('user_id' => "686,687") ,and z-ray print "select * from kd_oa_userinfo where user_id in ('686,687')"
//second time,i set the $sqlArg = array('user_id' => "686','687") ,and z-ray print "select * from kd_oa_userinfo where user_id in ('686','687')"

$result = $statement->execute($sqlArg);
$resultSet = new ResultSet;
$resultSet->initialize($result);
$result = $resultSet->toArray();
var_dump($result);//but the $result always be 686
exit();