Isset不使用post方法

Simple code working correctly: Form:

<form name="newad" method="post" enctype="multipart/form-data" action="betterplace.php">
<input type="file" name="delhi" required="required" value="delhi" onchange="javascript:this.form.submit();">
</form>
Action:
$mumbai=$_FILES['image']['tmp_name'];
$sql = " SELECT xyz FROM `dataperiod` WHERE cities LIKE '$mumbai' ";
if(!$result = $conn->query($sql)){
    die('There was an error running the query [' . $conn->error . ']');
}
/do the stuff

But for making empty property,i assigned isset code to this like:

<?php
if(isset($_POST) && !empty($_POST)) {
$mumbai=$_FILES['image']['tmp_name'];
$sql = " SELECT xyz FROM `dataperiod` WHERE cities LIKE '$mumbai' ";
if(!$result = $conn->query($sql)){
    die('There was an error running the query [' . $conn->error . ']');
}
/do the stuff
}
else{  
    header('location: home.php'); exit();
}
?>

But nothing showing or working.I think problem is not taking post element.Please help.

Do onchange="javascript:this.form.submit();" firing and redirect to betterplace.php occurs?

Anyway, isset($_POST) is wrong, $_POST is always set, but can be empty, so, as files are always transferred via POST/PUT, you need just something like:

if (isset($_FILES['delphi'])) {
    ...
}

Look closer at $_FILES['delphi']. Yours file input named delphi, not image (as u assumed in mumbai=$_FILES['image']['tmp_name'];):

<input type="file" name="delhi" ... >

So, finally:

<?php
    if (isset($_FILES['delphi']) && is_uploaded_file($_FILES['delphi']['tmp_name'])) {
        $mumbai = $_FILES['delphi']['tmp_name'];
        ...
    }

Or:

<?php
    if (is_uploaded_file($mumbai = @$_FILES['delphi']['tmp_name'])) {
        ...
    }