PHP和MySQL问题

Question

I was wondering how can I stop an empty value from being entered into my MySQL database in the example below which will enter nothing in to the database, so that my MySQL Default NULL value is displayed in the database?

if(empty($_POST['username'])){
    $u = NULL;
}

Answer 1

$u='NULL'

then your SQL query could be

UPDATE myTable(user) INSERT user=$u WHERE id='12345';

Don't forget to sanitize the data you received from the user!