$sql =~ s/(?<=select)\s*[^,]*?\s+as//gi ;
$sql =~ s/(?<=,)\s*[^,]*?\s+as//gi ;

##</code><code>##

$sql =~ s/(?<=select|,)\s*[^,]*?\s+as//gi ;

##</code><code>##

Variable length lookbehind not implemented in regex