Mysql Group by with if statement 3 conditions

i need help wit mySQL select. I need group by zhrtaskgrp.WBS Element,accolade.Project ID and some values that begins with number group by zhrtaskgrp.WBS Element only. I Tried

GROUP BY IF((z.``Project Description`` NOT LIKE '[0-9]%'), z.``WBS Element``, (z.``WBS Element``,a.``Project ID``))

But it doesn't work and when i try
GROUP BY IF((z.``Project Description`` NOT LIKE '[0-9]%'), z.``WBS Element``, (z.``WBS Element`` AND a.``Project ID``)) it doesn't give the same result.

Any idea how to fix this? Thanks