عرض عملي: استعلام واحد وخمسة فهارس وخمس خطط

خطوة بخطوة

1. Query: recent paid orders of one customer on the 10 M-row table; the baseline plan is a sequential scan.
2. Add a single-column index on customer_id; compare plan and time.
3. Add (customer_id, created_at DESC); the sort step disappears.
4. Add a partial index on status = 'PAID', then a covering index with INCLUDE; observe an index-only scan.
5. Planned mistake: create (created_at, customer_id); the planner ignores it for this query. Fix: reverse the column order.
6. Record plan type, buffers, and time for all five.

Prepares MID-012-LAB1.

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