SQL Runs Backwards: Read the Pipeline First
Explain the practical execution pipeline behind a basic SELECT query.
The name SELECT is a little misleading: the real discipline is building the right row set before choosing the display columns. Source rows FROM and JOIN answer one question: what rows are even eligible to exist in this query? If you join orders to customers, every later clause sees the combined row set produced by that join. A missing join condition or a many-to-many join can multiply rows before you ever aggregate. Row filters WHERE removes individual rows before grouping. It is the place for facts that are true or false on one row: date range, status, region, non-null fields,…
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