需求：根据user

UPDATe bx_well_device_user_select a
JOIN (
	SELECT
		device_user_select_id,
		device_id,
		user_id,
		enterprise_id,
		@rank :=
	IF
		( @gen = user_id, @rank + 1, 1 ) rank,
		@gen := user_id 
	FROM
		bx_well_device_user_select,
		( SELECT @rank := 0, @gen := NULL ) temp  #声明变量 rank为自增字段 gen为判断用户字段
	WHERe
		del_flag = '0' 
	ORDER BY
		user_id ASC 
	) b ON a.device_user_select_id = b.device_user_select_id 
	SET a.num = b.rank