・この辺はDBによって実装方法異なるので要注意。
使い方
SELECT
CURRENT_DATE - cast( '12 months' as INTERVAL ) AS "今日から一年前",
CURRENT_DATE - cast( '3 days' as INTERVAL ) AS "今日から三日前",
CURRENT_DATE + cast( '3 months' as INTERVAL ) AS "今日から3か月後",
CURRENT_DATE + cast( '10 days' as INTERVAL ) AS "今日から10日後"
参考
https://postgresweb.com/post-882
・現在の日時を取得する
https://zukucode.com/2017/11/postgresql-now.html