Laravel 4 db查询，因为if而导致db :: raw（）错误

Question

$data = DB::table('view_term_invoice')
            ->groupby('tenant_no')
            ->select(
                'tenant_no' , 
                DB::raw('count(distinct term_no) as term'),
                DB::raw('count(distinct invoice_no) as invoice_no'),
                //DB::raw("if(type_inv = 'M',count(distinct invoice_no),0) as invoice_m"),
                //DB::raw("if(type_inv = 'T',count(distinct invoice_no),0) as invoice_t"),
                DB::raw("sum(distinct grand_total) as grand_total")
            )
            ->get();

when i running this query on db::raw i got error because of if() inside db::raw when i running on phpmyadmin i got no issue , i don`t understand why suddenly i got this error