Set value to NULL in MySQL

Question

Don't put NULL inside quotes in your update statement. This should work:

UPDATE table SET field = NULL WHERE something = something

You're probably quoting 'NULL'. NULL is a reserved word in MySQL, and can be inserted/updated without quotes:

INSERT INTO user (name, something_optional) VALUES ("Joe", NULL);
UPDATE user SET something_optional = NULL;

UPDATE MyTable
SET MyField = NULL
WHERE MyField = ''

You should insert null, not the string of 'NULL'.

Use NULL (without the quotes around it).

UPDATE users SET password = NULL where ID = 4

if (($_POST['nullfield'] == 'NULL') || ($_POST['nullfield'] == '')) {
   $val = 'NULL';
} else {
   $val = "'" . mysql_real_escape_string($_POST['nullfield']) . "'";
}

$sql = "INSERT INTO .... VALUES ($val)";

if you put 'NULL' into your query, then you're just inserting a 4-character string. Without the quotes, NULL is the actual null value.