具有$ var數據的SQL更新列

Question

$newCity = $_POST['city']; 

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

我在嘗試使用變量的值更新mySql列UPDATE。 但是，當我檢查的價值，它更新，但一旦我刷新執行，它改變了值爲NULL

編輯：$theUser = a working session username

Answer 1

嘗試：

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

也請儘量篩選用戶輸入之前將其傳遞給查詢。

Answer 2

if(isset($_POST['city'])){ 
    $newCity = mysqli_real_escape_string($_POST['city']); 
    $theUser = mysqli_real_escape_string($userUser); // assuming you haven't escaped it already. 
    $query = "UPDATE users SET city = '$newCity' WHERE username = '$theUser'"; 
    $set = mysqli_query($con, $query); 
}