MYSQL重复记录排除法处理方式

SELECT
	tmp.user_id,
	tmp.course_id,
	tmp.type,
	tmp.expire_time,
	@rownum := @rownum + 1,

IF (
	@course_id = tmp.course_id ,@rank := @rank + 1,
	@rank := 1
) AS rank,
 @course_id := tmp.course_id
FROM
	(
		SELECT
			user_id,
			course_id,
			type,
			add_time,
			expire_time
		FROM
			xz_user_course
		WHERE
			user_id = 296154
		ORDER BY
			course_id ASC,
			expire_time DESC
	) tmp,
	(
		SELECT
			@rownum := 0,
			@course_id := 0,
			@rank := 0
	) a