php mysql UPDATE-kommandoen opdateres ikke

Jeg tror, at BookingID er et heltal, så din opdateringslinje skal være:

$updatequery = mysqli_query($con, "UPDATE booking SET FirstName='" . $_POST['txtfirstname'] . "' WHERE BookingID=" . $_POST['txtid'] . ""); //excute UpDate Query

EDIT: Jeg testede dit script, og problemet var, at du lukkede formularen uden for while-løkken. Nu virker det

<!DOCTYPE html> 

<head>
    <title>Edit Students</title>
</head>

<?php

        $user = 'root';     //Database username ("Root for xampp")
        $pass = '';             //Database password ("empty for exampp")
        $db = 'all_tests';      //Name of database

        $con = new mysqli('localhost', $user, $pass, $db) or die("Unable to connect");         //Create new data connection ('name of host/server', user, password, database name)

        if (isset($_POST['btnUpdate'])) {   //Once Update button pressed perform this  code

            $updatequery = mysqli_query($con, "UPDATE test_1 SET FirstName='" . $_POST['txtfirstname'] . "' WHERE BookingID='" . $_POST['txtid'] . "'"); //excute UpDate Query

        };  

        $sql = mysqli_query($con, "SELECT *FROM test_1"); //Select All from Booking

    //Create Headers for table

echo "<table border='1'>                
<tr>
    <th></th>
    <th>Booking ID</th>
    <th>First Name</th>

</tr>";

//Show Edit Form///////////////////////////////////////////////////////////////////////////////////////////////////
while($row = mysqli_fetch_array($sql)) {    //Run sql code till there are no more rows to import 

echo "<form method=post>";    //Run update code at top of this page

//Populate table with query (sql)

echo "<tr>";
    echo "<td> <input name='btnUpdate' type='submit' value='update' /> </td>";           //once press update row this button is apart of
    echo "<td> <input type='text' value=" . $row['BookingID'] . " name='txtid' /> </td>";
    echo "<td> <input type='text' value=" . $row['FirstName'] . " name='txtfirstname' /> </td>";

echo "</tr>";
echo "</form>";
}


echo "</table>";



mysqli_close($con);     //Close connection

?>