UNION ALL Examples in SQL

What UNION ALL does

Stack result sets without removing duplicates. SQL syntax can vary by database, but the pattern below is a useful starting point for reports and analysis.

Syntax or pattern

SELECT col FROM table_a UNION ALL SELECT col FROM table_b;

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5 practical examples

Use UNION ALL in a sales report

Apply the UNION ALL pattern to a sales table.

-- UNION ALL example for sales
SELECT customer_id, order_date, total_amount
FROM orders
WHERE total_amount > 100;

This shows how the UNION ALL pattern can support a simple sales analysis.

Use UNION ALL for customers

Apply the UNION ALL pattern to customer records.

-- UNION ALL example for customers
SELECT customer_id, email, status
FROM customers
WHERE status = 'Active';

This is useful when customer records need filtering, labeling or summarizing.

Use UNION ALL for products

Apply the UNION ALL pattern to product or inventory data.

-- UNION ALL example for products
SELECT product_id, product_name, category
FROM products;

Product tables are good practice data for this SQL pattern.

Use UNION ALL for monthly reporting

Apply the UNION ALL pattern to a monthly reporting query.

-- UNION ALL example for monthly reporting
SELECT DATE_TRUNC('month', order_date) AS month, SUM(total_amount) AS sales
FROM orders
GROUP BY DATE_TRUNC('month', order_date);

This turns row-level transactions into a report-friendly result.

Use UNION ALL during data checks

Apply the UNION ALL pattern to find data quality issues.

-- UNION ALL example for data checks
SELECT customer_id, COUNT(*) AS records
FROM orders
GROUP BY customer_id
HAVING COUNT(*) > 1;

This is a useful pattern for auditing data before building a report.

Common mistakes to avoid

Forgetting that SQL dialects vary across PostgreSQL, SQL Server, MySQL, BigQuery and SQLite.
Using SELECT * in production reports when only a few columns are needed.
Not checking join keys, duplicate rows or NULL values before trusting results.

FAQ

Will this SQL work in every database?

The idea is portable, but function names and date syntax may vary. Check your database dialect if a function is not recognized.

Should I use this in a report query?

Yes, if the pattern matches the business question and you have checked filters, joins and row counts.

Why does my result have too many rows?

The most common reasons are duplicate join keys, missing filters or grouping at the wrong level of detail.

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