In this lesson, you’ll learn how to use the
UNION operator to combine multiple
SELECT statements into one result set.
Most SQL queries contain a single
SELECT statement that returns data from one or more tables. SQL also enables you to perform multiple queries (multiple
SELECT statements) and return the results as a single query result set. These combined queries are usually known as unions or compound queries.
There are basically two scenarios in which you’d use combined queries:
• To return similarly structured data from different tables in a single query
• To perform multiple queries against a single table returning the data as one query
Tip: Combining Queries and Multiple WHERE ...