$db = mysqli_connect('localhost', 'my_user', 'my_password', 'my_db');
$sql="SELECT * FROM login";
here i connected and stored my database and set a sql command (which is now a string) into these two veriables.
if(mysqli_connect_errno()){
echo'Database connection failed with the following error: '.mysqli_connect_errno();
exit;
}
this is to check if the database is correctly connected, if not then it will show some errors.
$result = mysqli_query($db,$sql);
here i put the database and the sql command to run my query.
while($row = mysqli_fetch_array($result)){
echo $row['username'];
}
here finally outputting the usernames(username is one of the column in my table in this case) which matched with that query
i will suggest This Sql site to get a better understanding on sql queries and try to improve the secuirty because this is the basic point where hackers try to inject their attact most offenly.
Note : If your table's in the database are empty then it will not able to fetch anything