Adding new columns to a table using php/sql - php

Question

I'm trying to create a feature that allows me to add a new column to a table in my database using sql and php. I currently have a front end form, where the user can select what table they wish to alter and input boxes for adding a new column name. I also want to display the new version of the selected table (i.e. with the new column attached) My front and back end scripts look like this below.
sql10.html:
<form action="sql10.php" method="post">
<select id="category">
<option value="" disabled selected>Select your option</option>
<option id="customer" value="customer">Customer Table</option>
<option id="booking "value="booking">Booking Table</option>
<option id="bookingline" value="bookingline">Order Table</option>
<option id="package" value="package">Package Table</option>
</select>
<br><br>
Column Name: <input type="text" name="colname" placeholder="Insert New Column Name">
<br>
<input type="submit" value="Submit"> <input type="reset" value="Clear">
sql.php:
<?php
$conn = mysqli_connect("localhost", "######", "#####")
or die("Could not connect: " . mysqli_error($conn));
print "Successful Connection!";
mysqli_select_db($conn, '#####') or die ('db will not open' );
print " You have connected to the Assignment 3 database.<br>";
$category = $_POST["category"];
$newcolumn = $_POST["colname"];
$query1="ALTER TABLE $category ADD $newcolumn varchar(255)";
$query2 = "SELECT * FROM $category";
mysqli_query($conn, $query1) or die ("Invalid query");
echo "Success in database entry";
$numrows = mysqli_affected_rows($conn);
echo $numrows . "row updated<br>";
$result = mysqli_query($conn, $query) or die("Invalid query");
$num = mysqli_num_rows($result);
echo "<table border='1'><tr><th>Booking ID</th></tr>";
for($i=0; $i<$num; $i++) { //uses $num as loop end value
$row = mysqli_fetch_row($result);
echo "<tr><td>" . $row[0] . "</td></tr>";
}
echo "</table>";
mysqli_close($conn);
?>
As of using this code, I am not able to create a new column for tables. My database consists of multiple tables and I want the user to be able to select which table they wish to add a column to as well as enter the name of the new column. Can anybody see what the problem is?

Answer 1

I think your mistake is that your select tag doesn't have a name attribute. Remember that a form when is submitted, it takes the value of elements with the name attribute.
So, if you put in your HTML code <select id="category" name="category">, you will be able to catch its value in your sql.php query with $_POST["category"]; maybe the $_POST["category"] is arriving empty, and therefore you cannot execute the $query1 sentence.