SQL DISTINCT, GROUP BY, and HAVING: From Unique Values to Grouped Reports

After you learn aggregate functions, the next step is asking for summaries by category: totals by region, counts by status, averages by department, and so on.

SQL for Files helps you practice these reporting patterns locally in the browser before applying them to your own CSV, JSON, or Parquet files.

DISTINCT is useful when you want a clean list of unique values, such as every region that appears in a sales table.

SELECT DISTINCT region
FROM sales
ORDER BY region;

GROUP BY collects rows into groups before aggregate functions run. Instead of one total for the whole table, you get one total per group.

SELECT region, SUM(amount) AS total_amount
FROM sales
GROUP BY region
ORDER BY total_amount DESC;

WHERE filters individual rows before grouping. HAVING filters the grouped results after aggregate values exist.

SELECT salesperson, COUNT(*) AS sale_count
FROM sales
GROUP BY salesperson
HAVING COUNT(*) > 1;

1. Use DISTINCT to remove duplicate values.
2. Use GROUP BY to summarize sales by region.
3. Use HAVING to keep only groups that match aggregate conditions.