UNION, INTERSECT, EXCEPT
Set operations and dedup behavior. Practical PostgreSQL patterns for production queries.
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Set operations and dedup behavior. Practical PostgreSQL patterns for production queries.
SELECT email FROM app.customers
UNION
SELECT contact_email FROM app.suppliers;
SELECT email FROM app.customers
INTERSECT
SELECT email FROM app.newsletter_subscribers;
SELECT email FROM app.customers
EXCEPT
SELECT email FROM app.unsubscribed;When to reach for this: This pattern appears in application or reporting SQL you maintain.
SELECT email, 'customer' AS source FROM app.customers
UNION ALL
SELECT contact_email, 'supplier' FROM app.suppliers;What this demonstrates:
| Alternative | Use When | Don't Use When |
|---|---|---|
| ORM query builder | Team standardizes on one stack | Complex SQL becomes opaque |
| Materialized view | Repeat expensive aggregates | Needs refresh strategy |
| Warehouse replica | Heavy BI scans | Not for OLTP latency |
Use multiline template strings or SQL files; lint in CI.
When you need unique rows without aggregates.
Sort can use index order if query matches index columns.
Stack versions: This page was written for PostgreSQL 18.4 (stable 18, maintenance 17), pgvector 0.8+, PgBouncer 1.x, Patroni 3.x, and PostGIS 3.5+.
Reviewed by Chris St. John·Last updated Jul 19, 2026