Which expression would you use to filter orders within the last 30 days relative to today?

• A. order_date > NOW() - INTERVAL '30 days'
• B. order_date >= DATE '30 days ago'
• C. order_date > CURRENT_DATE - INTERVAL '30 days'
• D. order_date > ADD_MONTHS(CURRENT_DATE, -1)

Answer: (C)

The key idea is to define a rolling 30-day window based on today and keep only orders that fall within that window. Using the current date and subtracting 30 days gives a clear cutoff date. By comparing order_date to that cutoff with a strict greater-than, you select orders that occurred after that cutoff, i.e., within the most recent 30 days up to today. Using CURRENT_DATE helps keep the boundary simple and avoids time components that can complicate date comparisons if order_date is a date (or a timestamp that will implicitly cast). It also ensures the window stays fixed to 30 days, not to calendar months.

Other approaches either introduce a time component (NOW()) which can affect boundary behavior, or subtract a calendar month (ADD_MONTHS) which isn’t the same as 30 days, since month lengths vary. The chosen expression thus cleanly and reliably captures the intended 30-day period.