SQL indexing for EF Core apps: composite covering index for filter + ORDER BY (PostgreSQL)

-- ======================================================================
-- Q: Which index would you add?
--
-- A composite index with the equality columns first and the sort column last.
-- Verify with EXPLAIN (ANALYZE, BUFFERS). For large datasets use keyset
-- pagination (WHERE created_at < @lastSeen) instead of OFFSET.
-- ======================================================================

-- Query to optimize
SELECT id, order_number, total_net
FROM orders
WHERE customer_id = @c AND status = 'Open'
ORDER BY created_at DESC
LIMIT 20;

-- Composite covering index: equality columns first, sort column last
CREATE INDEX CONCURRENTLY ix_orders_customer_status_created
    ON orders (customer_id, status, created_at DESC)
    INCLUDE (order_number, total_net);   -- covering index