嗨，我是Oracle的新手。如何做一个简单的陈述，例如从最近30天或20天的购买日期获取产品ID？
SELECT productid FROM product WHERE purchase_date ?
SELECT productid FROM product WHERE purchase_date > sysdate-30
SELECT productid FROM product WHERE purchase_date ?
SELECT productid FROM product WHERE purchase_date > sysdate-30
