query.sql

DESC
SELECT
  name
FROM
  accounts 
WHERE
  del_flg = 0
AND creation_time < '2016/10/29 00:00'
AND RAND() < (SELECT (CAST(10 AS DOUBLE) / COUNT(id) * 10) FROM accounts WHERE del_flg = 0 AND creation_time < '2016/10/29 00:00')
LIMIT
  10

result.md

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	accounts	range	del_flg,creation_time,creation_time_del_flg_name	creation_time_del_flg_name	4	\N	1561090	Using where; Using index
2	SUBQUERY	accounts	range	del_flg,creation_time,creation_time_del_flg_name	creation_time_del_flg_name	4	\N	1561090	Using where; Using index