我的表在页面重新加载时用空行更新

I have made a basic example with a form and some PHP/JavaScript code. I'm validating the form using JavaScript and using PHP simply to update MySQL table.

function checkForm(){
    var x = document.forms['form1']['first'].value;
    if(x=='' || x==null){
        alert('please finish all required fields');
        return false;
    }
    var y = document.forms['form1']['last'].value;
    if(y=='' || y==null){
        alert('please finish all required fields');
        return false;
    }
    var z = document.forms['form1']['email'].value;
    if(z=='' || z==null){
        alert('please finish all required fields');
        return false;
    }   
    var a = document.forms['form1']['phone'].value;
    if(a=='' || a==null){
        alert('please finish all required fields');
        return false;
    }   
}

</script>
</head>
<body>
<?php

$connect = mysqli_connect('localhost','colin','-koolio-','knoxprograms');
if(mysqli_connect_errno()){
    echo "Error " . mysqli_connect_error();
}


$first = mysqli_real_escape_string($connect, $_POST['first']);
$last = mysqli_real_escape_string($connect, $_POST['last']);
$email = mysqli_real_escape_string($connect, $_POST['email']);
$phone = mysqli_real_escape_string($connect, $_POST['phone']);

$sql = "insert into users(firstName, lastName, email, phone) VALUES('$first','$last','$email','$phone');";

mysqli_multi_query($connect, $sql);
?>

<form name="form1" method="post" action="fuckwithpage.php" onsubmit="return checkForm()">
First name: <input type="text" name="first"><br>
Last Name: <input type="text" name="last"><br>
email: <input type="text" name="email"><br>
phone: <input type="text" name="phone"><br>
<input type="submit" value="send">
</form>

The JavaScript validation that occurs when the form is submitted(submit button is clicked) prevents my table from being updated if my validation function for the form returns false. However if the page is reloaded or when i load the page, an empty row is added to my table. can anyone assist me with this.

Begin your php with:

if ($_POST) {  //[...your code, here...]  }

Otherwise, every time the page is loaded, that block of code will fire - since there's nothing telling it "Hey, we're just loading the page, nothing has been submitted yet, so don't do anything - " - that is the role that the above conditional statement will fill.

    if (isset($_POST)){    
$first = mysqli_real_escape_string($connect, $_POST['first']);
$last = mysqli_real_escape_string($connect, $_POST['last']);
$email = mysqli_real_escape_string($connect, $_POST['email']);
$phone = mysqli_real_escape_string($connect, $_POST['phone']);

$sql = "insert into users(firstName, lastName, email, phone) VALUES('$first','$last','$email','$phone');";

mysqli_multi_query($connect, $sql);
}

Try That CMIIW :))