This one took me a minute to settle on an approach.
Start by clarifying the schema and the expected output, then outline a query that aggregates each event table separately and joins the results to the servers table using LEFT JOINs. Emphasize the use of COALESCE or IFNULL to convert NULL counts to zero, ensuring servers with no events are included with zero totals.
Pro tip: Mention that pre-aggregating each event table in subqueries or CTEs avoids fan-out and improves performance, especially at Discord's scale. Also, note that using COUNT(column) instead of COUNT(*) in the subqueries can be more efficient if there are nullable columns.
Confirm the table structures, the definition of 'all-time', and whether the output should include servers with zero events. Ask if there are any filters or time constraints.
Plan to aggregate each event table (views, joins, messages) separately to get counts per server_id. This prevents incorrect counts due to joining multiple one-to-many relationships.
Use LEFT JOINs from the servers table to the aggregated subqueries, and apply COALESCE to replace NULLs with 0. Ensure the query returns one row per server.
Explain that LEFT JOIN combined with COALESCE handles servers with no events, and discuss alternative approaches like UNION or FULL OUTER JOIN if needed.
Mention indexing on server_id in event tables, the cost of aggregating large tables, and potential optimizations like materialized views or pre-aggregated tables.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.