CASE & UNION: one report, many sources

READ & UNDERSTAND

A JOIN adds related columns to a row. UNION ALL appends the rows from another SELECT. Before combining sources, write the output columns in order and say what each means. Same column count is necessary, but same meaning and compatible values are just as important.

For a small product-and-event directory, agree on label, dollars and source. The event name must land under label and its fee under dollars. SQLite may accept a swapped text/number position, producing a report that runs with misleading cells.

Aliases for the combined output come from the first SELECT. Apply one ORDER BY at the end using those output names. A source literal tells readers where the row came from; a shared numeric ID by itself does not identify a record across different tables.

SELECT title AS label, shelf_price AS dollars, 'Game' AS source FROM games WHERE id <= 2 UNION ALL SELECT name, fee, 'Event' FROM events WHERE id <= 2 ORDER BY source, label;

Your question

Build a directory of games with id <= 3 and events with id <= 3. Return label, dollars, source (Game or Event), using UNION ALL. Order by source, then label.

Explain your evidence

Why can a query have the expected row count and still violate its column contract?

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