This one tripped me up more than I expected.
First, clarify the requirements: the query should return the week start date (Monday) and total event count for each ISO week that falls entirely within the previous calendar month relative to the current date parameter. Then, filter the daily event counts to only include dates in that previous month, and group by the ISO week start date, summing the counts.
Pro tip: Mention that ISO weeks start on Monday and that the week start date should be calculated using date functions like DATE_TRUNC('week', event_date) in PostgreSQL or equivalent. Also, note that if a week spans across month boundaries, it should be excluded because it doesn't fall entirely within the previous month.
Confirm that 'previous calendar month' means the full month immediately before the current date, and that 'ISO week' means weeks starting on Monday. Also, clarify that only weeks entirely within that month should be included.
Calculate the first and last day of the previous calendar month based on the current date parameter. For example, if current date is '2024-03-15', the previous month is February 2024, so start date is '2024-02-01' and end date is '2024-02-29'.
Filter the daily event counts to only include rows where event_date is within the previous month. Then, compute the ISO week start date (Monday) for each event_date using a date function like DATE_TRUNC('week', event_date).
Group the filtered data by the computed week start date and sum the event counts to get the total for each ISO week.
Add a condition to only include weeks where the week start date is >= first day of previous month and the week end date (week start + 6 days) is <= last day of previous month. This ensures the week falls entirely within the previous month.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.