Editing SQL (section)

== <span style="color: #FFFFFF;">Applying</span> ==
Common patterns:

; Basic retrieval
:<code>SELECT name, email FROM users WHERE active = 1 ORDER BY created_at DESC LIMIT 10;</code>

; Joining tables
:<code>SELECT orders.id, users.name, orders.total
FROM orders
JOIN users ON orders.user_id = users.id
WHERE orders.status = 'shipped';</code>

; Aggregation
:<code>SELECT product_id, COUNT(*) AS num_orders, SUM(total) AS revenue
FROM orders
GROUP BY product_id
HAVING SUM(total) > 1000
ORDER BY revenue DESC;</code>

; Subquery
:<code>SELECT name FROM users
WHERE id IN (SELECT user_id FROM orders WHERE total > 500);</code>

; Upsert (insert or update)
:<code>INSERT INTO settings (user_id, key, value)
VALUES (42, 'theme', 'dark')
ON CONFLICT (user_id, key) DO UPDATE SET value = EXCLUDED.value;</code>

; Common Table Expression (CTE)
:<code>WITH recent_orders AS (
  SELECT * FROM orders WHERE created_at > NOW() - INTERVAL '30 days'
)
SELECT user_id, COUNT(*) FROM recent_orders GROUP BY user_id;</code>

Practical habits: always filter early (move conditions as close to the source as possible), use EXPLAIN to inspect the query plan before deploying, and never run UPDATE or DELETE without a WHERE clause in production.
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