How to update record if not empty and set initial value if empty

Question

How do i update a record when the post value is not empty, and it the post is empty i will set it with the default value.

user table

id   |  key  | date
-----|-------|-------------
100  | 2     | 26/03/2017
     |       |

MY PHP

<?php
$setKey = (isset($_POST['change_key']) ? $_POST['key'] : null);
$handler = $conn->prepare("
   UPDATE user SET key = IF(key IS NOT NULL, :key, NULL), 
   date = :date 
   WHERE id = :id
");
$handler->bindParam(':key', $setKey);
$handler->bindParam(':date', $_POST['date']);
$handler->bindParam(':id', $_POST['id']);
?>

From the above example i want if $setKey is null the sql will update the date and other columns and set the KEY to the current value which is 2 from the above example.

Answer 1

<?php
$setKey = (isset($_POST['change_key']) ? $_POST['key'] : null);
$handler = $conn->prepare("
   UPDATE user SET key = IFNULL(:key, NULL), 
   date = :date 
   WHERE id = :id
");
$handler->bindParam(':key', $setKey);
$handler->bindParam(':date', $_POST['date']);
$handler->bindParam(':id', $_POST['id']);
?>