When the user did not fill up all the blanks or fill in wrongly, how to validate them and bring it back to the same form?

Question

This is by Newcustomer.php form whereby i click on the button next, it will proceed to the next form which is NewExpertise.php.

<form action = NewExpertise.php method="post">
    <?php
    include('CSS.php');
    include('DB.php');
    ?>
    <span class =wordtab>Name</span> <input name = newname id = 'newname' type='text'/> <br>
    <span class =wordtab>IC</span><input name = newic id = 'newic' type='text'/><br>
    <span class =wordtab>Number</span><input name = newnumber id = 'newnumber' type='text'/><br>
    <span class =wordtab>Nationality</span><input name = newnationality id = 'newnationality' type='text'/><br>
    <span class =wordtab>Status</span>
    <select name = 'newstatus' id = newstatus>
        <option value="Interested">Interested</option>
        <option value='Not Interested'>Not Interested</option>
    </select><br>

    <span class =wordtab>Remarks</span><input name = newremarks id = 'newremarks' type='text'/><br>
    <?php

    ?>
    <br><br>

    <input type="submit" id="Next" name="Next" value = "Next" >
    <br><br>
    <input type="button" onclick="location.href='index.php';" value="Back to CRM" />
    </form>

This are my codes from newexpertise.php. It shows an sql to insert the new customer into my database. However i did a validation whereby if the textboxes are empty, i want it to go back to newcustomer.php and prompt them what fields are missing. If possible, how can i also validate fields whereby user and only type in numeric values in number textbox for example. Thank you so much.

    if(isset($_POST['Next']))
    {
        if($_POST['newname']==""||$_POST['newic']==""||$_POST['newnumber']==""||$_POST['newnationality']==""||$_POST['newstatus']==""||$_POST['newremarks']=="")
        {
            $message = "Please fill in the all the relevant data";
            echo "<script type='text/javascript'>alert('$message');</script>";

        }

        else
        {

            $addquery = "INSERT INTO Particulars (Particulars_ID, Name, Identification_Number, Number, Nationality, Status, Remarks)
                    VALUES(LAST_INSERT_ID(),'$_POST[newname]', '$_POST[newic]','$_POST[newnumber]','$_POST[newnationality]','$_POST[newstatus]','$_POST[newremarks]')";
            if ($connect->query($addquery) === TRUE)
            {
                    $last_id = $connect->insert_id;


            }


            else 
            {
                echo "Error updating record: " . $connect->error;
            }

        }
    }


    ?>

Answer 1

I would do the following: Post your newcustomer formula to newcustomer.php. if it validates use

header("Location: http://test.com/nextpage");

To redirect the user. If validation fails use this code to write the users values back into the form

<input id="test" name="test" value="<?php    if(isset($_POST["test"])){echo $_POST["test"]}?>"/>