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Outer join + date filter — predicate placement

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Outer join + date filter — predicate placement

Pin 2026-05-25T12:00:00Z as "now". Return every order, with its refund info if a refund occurred in the last 30 days (refund_ts >= 2026-04-25T12:00:00Z). Orders with no qualifying refund must still appear — with NULL refund columns.

The trap: putting the date filter in WHERE instead of in ON turns the LEFT JOIN into an INNER JOIN — orders without recent refunds disappear. Place the filter inside the ON clause to preserve them.

Columns: order_id, refund_id, strftime(refund_ts, '%Y-%m-%d %H:%M:%S') AS refund_ts. (The strftime keeps the timestamp comparison string-stable for grading.) Sort by order_id ascending.

Tables & sample data

orders

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refunds

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query.sql

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