UNION combines results from multiple SELECT statements into a single result set.

Basic UNION

SELECT name, email FROM customers

UNION

SELECT name, email FROM suppliers;

UNION vs UNION ALL

-- UNION removes duplicates

SELECT city FROM customers UNION SELECT city FROM suppliers;

-- UNION ALL keeps duplicates (faster)

SELECT city FROM customers UNION ALL SELECT city FROM suppliers;

UNION with Different Tables

SELECT 'Customer' as type, name, email FROM customers

UNION

SELECT 'Employee' as type, name, email FROM employees;

UNION with ORDER BY

SELECT name, created_at FROM customers

UNION

SELECT name, created_at FROM suppliers

ORDER BY created_at DESC;

UNION Rules

Same number of columns

Compatible data types

Column names from first query

Generate UNION Queries

AI2sql combines multiple data sources effortlessly.