Increment MySQL row value based on PHP form submission

Question

I have a simple form, and a MySQL table set up.

All I am trying to do is every time the form is submitted add 1 onto the selected row amount.

Table is as simple as:

    answer | amount
------------------------
    Yes    | 5
    No     | 12
    Maybe  | 1

And the form is:

<form action="submit.php" method="post">
Is this a cool pie chart?:
<input type="radio" name="group1" value="Yes"> Yes<br>
<input type="radio" name="group1" value="No"> No<br>
<input type="radio" name="group1" value="Maybe"> Maybe<br>
<input type="submit">
</form>

Then in submit.php I have the following so far, but doesn't seem to be working

 <?php
    $sql = "UPDATE results SET amount= amount + 1 where answer = ?";
    $stmt = mysqli_prepare($conn, $sql);
    mysqli_stmt_bind_param($stmt, "s", $selected_option);   

    if (isset($_POST['submit'])) {
         $selected_option = $_POST['group1'];
         if ($selected_option == 'Yes') {
                mysqli_stmt_execute($stmt);
          }else if ($selected_option == 'No') {
                mysqli_stmt_execute($stmt);
          } else if ($selected_option == 'Maybe')
             mysqli_stmt_execute($stmt);
    }
?>

So if someone answers yes the amount row for yes will increase to 6 etc etc.

I have managed to call the data and even add it into the Google Visualization API using tutorials, but seem to failing at this part.

Thanks in advance everyone.

I have made an edit to include the submit.php code so far, not even sure if i'm on the right path :/ — Damian Smith
– Damian Smith, Commented Aug 6, 2013 at 10:51

contradictioned · Accepted Answer · 2013-08-06 11:11:08Z

1

If you issue the query

UPDATE results SET amount = amount + 1

you will update the amount-value of every line in the table. So you have to specify the row with a WHERE-predicate:

UPDATE results SET amount = amount + 1 WHERE answer = ?

The value for ? should be the posted value of the group1-variable. In order to prevent SQL injection do this as a prepared statement ( see http://php.net/manual/de/pdo.prepared-statements.php )

answered Aug 6, 2013 at 11:11

contradictioned

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2 Comments

Damian Smith Over a year ago

I have updated my code as shown above but doesn't actually update the table. Must be something minor now thats stopping it from working :/

Damian Smith Over a year ago

Ok got it working! was purely the brackets wrapped around the amount = amount + 1 that stopped it... don't know why I had that! Thanks for your help

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