mysqli_change_user does not allow to use NULL for $database param

[kamil-tekiela]

Description

According to the documentation, the third parameter in mysqli_change_user is nullable (not optional though) and passing NULL should connect to the same database.

If desired, the null value may be passed resulting in only changing the user and not selecting a database. To select a database in this case use the mysqli_select_db() function.

But to my knowledge this was never possible and is still not supported by mysqli. This code will reset database to NULL

$mysqli = new mysqli("localhost", "my_user", "my_password", "test");
$mysqli->change_user("my_user", "my_password", null);
var_dump($mysqli->query("SELECT DATABASE()")->fetch_row()[0]);

Resulted in this output:

NULL

But I expected this output instead:

string(4) "test"

PHP Version

All versions

Operating System

No response

[damianwadley]

The function works how it was designed, but the documentation was unclear.

Correct, as far as I can see: mysqli proxies to mysqlnd which I assumes eventually gets to mysql_change_user, where they say

Pass a db parameter of NULL if you do not want to have a default database.

which sounds more like "don't use any default database" than it does "don't specify which database to start using".