SELECT GROUP_CONCAT(CAST(coupon_amount as SIGNED) separator ',')

FROM ellabook_coupon WHERE coupon_subject_id=#{couponSubjectId,jdbcType=VARCHAR}

AND member_id=(SELECT member_id FROM ellabook_coupon

WHERE coupon_subject_id=#{couponSubjectId,jdbcType=VARCHAR} GROUP BY member_id LIMIT 0,1)