Customers who ordered in every month of Q3

A retention analyst wants the most consistent buyers: customers who placed at least one order in each of July, August and September 2026.

From store_orders, return customer_id, orders_in_quarter and total_spent (both counting only orders from 1 July to 30 September 2026) for customers active in all three months. Order by customer_id.

1. Step 1: Restrict the rows to the quarter in `WHERE` first. Without it, customer 2 (July, September and October orders) would also count three distinct months.
2. Step 2: `COUNT(DISTINCT DATE_TRUNC('month', order_date))` counts how many different months a customer ordered in.
3. Step 3: Requiring that count to equal 3 in `HAVING` keeps customers active in every month; customer 6's June order is excluded by the date filter, so their totals cover Q3 only.

SELECT customer_id,
       COUNT(*)           AS orders_in_quarter,
       SUM(order_amount)  AS total_spent
FROM store_orders
WHERE order_date >= DATE '2026-07-01'
  AND order_date <  DATE '2026-10-01'
GROUP BY customer_id
HAVING COUNT(DISTINCT DATE_TRUNC('month', order_date)) = 3
ORDER BY customer_id;