Result order without ORDER BY

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Accepted Answer

Without ORDER BY, the SQL standard makes no guarantee about row order. The database is free to return rows in whatever order is most efficient - heap scan order, index scan order, or something else entirely. In practice the order often looks consistent across repeated runs, which fools people into depending on it. Any code that relies on unordered output is a latent bug waiting to surface after an index change, a vacuuming event, or a schema migration.