Difference Between UNION and JOIN in Oracle SQL

When working with Oracle SQL, it is important to distinguish between the UNION and JOIN operators, as they serve different purposes in combining data from multiple tables.

UNION Operator

The UNION operator is used to combine the result sets of two or more SELECT statements into a single result set. It removes duplicate rows from the combined result set and orders the results in ascending order by default.

JOIN Operator

On the other hand, the JOIN operator is used to retrieve data from multiple tables based on a related column between them. There are different types of JOIN operations in Oracle SQL, such as INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN, each with its own way of combining data from the tables.

Key Differences

• UNION combines result sets vertically, while JOIN combines data horizontally from different tables.
• UNION removes duplicate rows, while JOIN combines tables based on a specified condition.
• UNION can combine result sets from different queries with the same number of columns, while JOIN requires a common column to establish a relationship between tables.

Understanding the difference between the UNION and JOIN operators is essential for writing efficient and effective queries in Oracle SQL.