每一个分类读4个文章，怎么样写SQL

select * from courses where courses.category_id = '1' order by id desc limit 4
select * from courses where courses.category_id = '2' order by id desc limit 4
select * from courses where courses.category_id = '3' order by id desc limit 4
select * from courses where courses.category_id = '4' order by id desc limit 4

我现在都是重复来写的