How do I delete either the first or last set of rows in a dynamic fashion

Question

I would like to delete the first 100 rows or the last 100 rows in a certain table (ordered by the primary key).

Note: Lots of data is being spooled into this table.<

Answer 1

SET @first = 1;
delete from mytable 
where primKey in (select 1 
                  from myTable 
                  order by 
                    CASE WHEN @first = 1 THEN primKey END ASC,
                    CASE WHEN @first <> 1 THEN primKey END DESC
                  limit 100)