Finding duplicates

Study the pattern

GROUP BY and HAVING COUNT(*) > 1 identifies repeated values. Predict the output before running the example.

SELECT customer_id,COUNT(*) AS order_count FROM orders GROUP BY customer_id HAVING COUNT(*)>1 ORDER BY customer_id;

Explain it from memory

What does today's SQL feature do, and when would you use it?

Group by customer_id and filter with HAVING COUNT(*) > 1.

Run SQL in your browser

Run the example, then modify one clause and predict how the result changes.

Group by customer_id and filter with HAVING COUNT(*) > 1.

Consolidate the skill

• Run and inspect the output.
• Change one part and predict the difference.
• Return later and rewrite the query from memory.