MySQL分组查询指定列最新的数据

		SELECT
		i.add_time,
		i.id AS procInstId,
		latestTask.action,
		type_id,
		type_name,
		i.user_id,
		i.user_name,
		i.`status`
		FROM
		flow_proc_inst i
		LEFT JOIN (
				SELECT
				maxLine.*, MAX(maxLine.step) maxStep
				FROM
				(SELECT DISTINCT(t1.id) tt,t1.* FROM flow_task t1 ORDER BY t1.step DESC
				) maxLine
				GROUP BY
				maxLine.proc_inst_id
			) AS latestTask ON latestTask.proc_inst_id = i.id
		WHERE
		i.user_id = #{c.userId}