What is the purpose of the union operation in databases?

The union operation in databases is used to combine the results of two or more SELECT queries into a single result set. It merges distinct records from multiple tables or queries, ensuring that the output retains only unique entries – meaning duplicate rows are eliminated. This is particularly useful when you want to aggregate data from different sources that share the same structure, such as the same number of columns and compatible data types in each column.

The effectiveness of the union operation lies in its ability to provide a cohesive view of data that may be stored in different tables, making it easier to analyze and report on combined datasets without duplicates. By focusing on the distinct records, it allows for more concise and informative outputs when managing relational databases.