UNION in Oracle - Examples & AI Generator

Combining results from multiple SELECT queries with UNION in Oracle can be complex, especially when working across different database systems. Oracle's UNION is case-insensitive, removes duplicates by default, and requires compatible column types and counts. But what if you could skip memorizing Oracle or other SQL dialects altogether? With AI2sql - AI SQL Generator, you can turn natural-language requests into production-ready UNION queries—no coding required and instant results.

UNION Syntax in Oracle

Basic Syntax

SELECT column1, column2 FROM table1
UNION
SELECT column1, column2 FROM table2;

• Each SELECT must have the same number of columns and types.

• Duplicate rows are removed by default.

• For all rows (including duplicates), use UNION ALL instead.

UNION Examples You Can Generate Instantly

1. Combine Customers From Two Regions

SELECT customer_id, customer_name FROM customers_us
UNION
SELECT customer_id, customer_name FROM customers_eu;

Get a unified list of customers from US and EU tables—duplicates removed automatically.

2. Merge Orders From Last Year and This Year

SELECT order_id, order_date FROM orders_2023
UNION
SELECT order_id, order_date FROM orders_2024;

See every unique order placed across two years in one result set.

3. List All Product IDs From New and Legacy Catalogs

SELECT product_id FROM products_legacy
UNION
SELECT product_id FROM products_new;

Identify all unique products available, regardless of which table they're in.

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• No syntax memorization: Skip the Oracle-specific UNION rules.

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FAQs About UNION in Oracle

What is the difference between UNION and UNION ALL in Oracle?

UNION removes duplicate rows, while UNION ALL includes all results from both queries, including duplicates. Use UNION ALL if you don't want duplicates removed.

Why do column counts need to match in Oracle UNION?

Each SELECT must return the same number and compatible types of columns because Oracle merges the results vertically. A mismatch triggers an error.

Can I use ORDER BY with Oracle UNION queries?

Yes, but you should add ORDER BY at the end of the last SELECT to sort the final combined result set, not within individual SELECTs.

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