How to clear a variable value correctly?

[CGTroll]

What is the best way to clear a value in a table?

Scenario:

If user choose to delete article image, the filename in the table should be cleared.

 

I have used $old_image = ""; to clear the name and then update table, but that doesn't seem to clear the value completely, as when I do a check afterwards if filename was deleted by using statement if($filename), it always return True, as in, there is a value present for $filename even when name has been cleared. 

 

Have a got this correct or is there something else I am missing,

 

In advance, thanks!

[Ron916]

unset($old_image);

Edited August 16, 2013 by Ron916

[CGTroll]

Thanks!