CASE & UNION: one report, many sources

READ & UNDERSTAND

UNION removes rows identical across every selected column; UNION ALL retains every row. Duplicates are a property of the selected output, not proof that the source contains duplicate records. Two different sessions can have the same member and day.

Choose the unit of the report first. A list of distinct days needs deduplication; a list of recorded actions should preserve repeats. Add source and source_id when you need to trace each action back to its original table.

For an audit sample, inspect member 3 on 2026-09-12. Repeated sessions and orders are real source records. A source label separates orders from sessions, but alone it cannot distinguish two sessions on that same day. UNION ALL preserves both even when the display columns match.

SELECT id, member_id, session_date FROM sessions WHERE member_id = 3 AND session_date = '2026-09-12' ORDER BY id;

Your question

Return every session and café order for member 3 on 2026-09-12 as source (Session or Order), source_id and activity_date. Use UNION ALL and order by source, source_id.

Explain your evidence

If source_id is removed, which rows become indistinguishable? Does an identical display mean the member acted only once?

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