MySql/PHP data not getting removed - php

Question

<?php
session_start();
//get the location name/address.
$address = $_POST['table'];
$_SESSION['myaddress'] = $address;
$username = $_SESSION['username'];
//connection details.
$sev_host = "localhost";
$sev_username = "root";
$sev_password = "";
$sev_db = "mydata";
//Connecting server with db.
$conn = mysqli_connect($sev_host, $sev_username, $sev_password, $sev_db);
if (!$conn) {
die("Error : " . mysqli_connect_error());
}
//Check if the table exist, and if not then create the table
$pre_check = "select location from users where username='$username";
$result_pre_check = mysqli_query($conn, $pre_check);
$pre_remove = "delete from $result_pre_check where username='$username'";
mysqli_query($conn, $pre_remove);
$pre_insert = "update users set location='$address' where username='$username'";
mysqli_query($conn, $pre_insert);
$sql = "CREATE TABLE $address (id int(6) unsigned auto_increment primary key, username varchar(255) not null, src varchar(255) not null)";
$sql2 = "INSERT INTO $address (id, username, src) VALUES ('', '$username', '')";
mysqli_query($conn, $sql);
mysqli_query($conn, $sql2);
?>
This is my php code, and I seem to have a problem in it. This code is attached to a button and runs when it is clicked, but it's not giving me the required result. As you can see that I am deleting a row on $pre_remove statement, but when the code runs everything works except that the required row is not removed from the table.
The code works fine and it doesn't give out any debug errors. Any ideas?

Answer 1

The reason this doesn't work lies within your query on $pre_remove
A good way to debug your code, would be to use functions like var_dump, print_r etc. to see what your variables actually contains.
In this specific case, the problem lies within delete from $result_pre_check
$result_pre_check is not a variable. Again, you can do a var_dump($result_pre_check) to see what this variable is / contains.
Your query to delete a user based on username would however work if it was:
$pre_remove = "delete from users where username='$username'";

Answer 2

You can try something like this,
$pre_remove = "DELETE FROM users WHERE username IN (
SELECT location FROM users WHERE username='$username'
)";
mysqli_query($conn, $pre_remove);
instead of ,
$pre_check = "select location from users where username='$username";
$result_pre_check = mysqli_query($conn, $pre_check);
$pre_remove = "delete from $result_pre_check where username='$username'";
mysqli_query($conn, $pre_remove);