带有$ var数据的SQL Update列

Question

$newCity = $_POST['city'];

$set = mysqli_query($con, "UPDATE users SET city = '$newCity' WHERE username = '$theUser'");

I'm trying to update mySql column through UPDATE using a value of a variable. But when I check the value, it updates, but once I refresh the execute, it changes the value to NULL

Edit: $theUser = a working session username

Answer 1

Try:

if(isset($_POST['city'])){
 $newCity = $_POST['city'];
 $set = mysqli_query($con, "UPDATE users SET city = '$newCity' WHERE username = '$theUser'");
}

Also please try to filter your user input before passing it to query.