PHP (here if statement) in server side script possible?

Hi.

I give some variables to my server side script and want to make a where condition only if variable is set.

Can I make a php if statement in this script? Or is there another solution?

I need this and this is not working:

if($aktiv == '1'){
         ->where( 'tm_pflegestellen.Aktiv', $aktiv, '=')
}
if($schulung == '1'){
         ->where( 'tm_pflegestellen.Schulung', '0000-00-00', '=')
}

Thanks
Rappi