包含在函数中时，php语句无法正常工作

Question

下面的代码在没有包含在函数

中时工作正常

$opt = 'logo_img';
$sql="SELECT option_value FROM r0_options WHERE option_name='".$opt."'";
$result=mysqli_query($db,$sql);
$row=mysqli_fetch_array($result,MYSQLI_NUM);
var_dump($row);

但是，当我执行以下操作并调用该函数时，它会给出NULL。

function get_result($opt){
    $sql="SELECT option_value FROM r0_options WHERE option_name='".$opt."'";
    $result=mysqli_query($db,$sql);
    $row=mysqli_fetch_array($result,MYSQLI_NUM);
    var_dump($row);
}

get_result('logo_img');

Answer 1

It's because you are not passing $db variable, either pass it to function or do the following:

function get_result($opt){
    global $db;

    $sql="SELECT option_value FROM r0_options WHERE option_name='".$opt."'";
    $result=mysqli_query($db,$sql);
    $row=mysqli_fetch_array($result,MYSQLI_NUM);
    var_dump($row);
}

get_result('logo_img');

Answer 2

You are forgotten to pass he '$db' to your function:

function get_result($db, $opt){