Posts tagged “SQL”
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Using a PostgreSQL table as a job queue: FOR UPDATE SKIP LOCKED and when the lock is released
How FOR UPDATE SKIP LOCKED lets several workers share jobs in one PostgreSQL table, per the official docs: lock lifetime, LIMIT and OFFSET, ORDER BY, and locking clauses inside WITH.
Why two SELECTs in one transaction can disagree: PostgreSQL READ COMMITTED and snapshots
Under PostgreSQL's default READ COMMITTED level, two SELECTs in one transaction can see different data. Learn how statement snapshots, row rechecks, and transaction retries work.
Why NOT IN returns no rows: SQL NULL and three-valued logic
One NULL in a subquery makes NOT IN return zero rows. Why, per the PostgreSQL, MySQL and SQLite docs: three-valued logic, how WHERE keeps rows, and fixing it with NOT EXISTS.
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