SELECT
MEMBER_ID AS ID
--点数1回目から点数2回目を引いた値
,SCORE1 - SCORE2 AS DIFF
FROM CONTEST_RESULTS

WHERE
ABS(SCORE1 - SCORE2) >= 20

ORDER BY
--表示項目DIFFの降順
(SCORE1 - SCORE2) DESC
--表示項目IDの降順
,MEMBER_ID DESC
;