Combine the tuples of two relations.
The Union operation, denoted by the symbol ∪, is a binary operation in relational algebra that combines the tuples from two relations into a single new relation. For the Union operation to be valid, the two input relations must be 'union-compatible'. This means they must have the same number of attributes, and the domains (data types) of the corresponding attributes must be compatible. For example, you can take the union of a 'Faculty' table and a 'Staff' table if both have compatible columns like 'person_id' and 'name'. The result of R ∪ S is a relation that contains all tuples that are in R, or in S, or in both. Similar to the Project operation and standard set theory, the Union operation automatically eliminates duplicate tuples. If a tuple exists in both input relations, it will appear only once in the resulting relation. This operation is useful for consolidating information from different tables that share a common structure. For example, you could get a single list of all people in a university by taking the union of the 'Students' relation and the 'Employees' relation (assuming they are made union-compatible, perhaps by projecting onto common attributes first). The SQL equivalent of this operation is the `UNION` operator.