Chapter 6: Problem 2

What is union compatibility? Why do the UNION, INTERSECTION, and DIFFER. ENCE operations require that the relations on which they are applied be union compatible?

Short Answer

Expert verified

Union compatibility refers to the equivalence in structure of two or more relations, meaning they have the same number of columns and the corresponding columns have the same or compatible domains. The UNION, INTERSECTION, and DIFFERENCE operations require union compatibility because they involve comparing or combining tuples from two or more relations, which would be unclear or impossible if the relations had different or incompatible structures.

Step by step solution

Define Union Compatibility

Union Compatibility in database refers to the equivalence in structure of two or more relations. These relations (or tables, in DB language) are said to be union compatible if they have the same number of columns and the corresponding columns have the same or compatible domains.

Explain need of Union compatibility for UNION operation

The UNION operation combines the tuples of two relations and removes any duplicates. This can only be done if the relations are union compatible, otherwise it would be unclear how to combine different or incompatible columns.

Explain need of Union compatibility for INTERSECTION operation

The INTERSECTION operation returns all common tuples from two relations. This requires the relations to have compatible structure (union compatibility) , to accurately identify the common tuples.

Explain need of Union compatibility for DIFFERENCE operation

The DIFFERENCE operation identifies the tuples that are present in one relation but not in the other. This requires the relations to be union compatible, otherwise it would be unclear how to compare each tuple from the relations.

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What is union compatibility? Why do the UNION, INTERSECTION, and DIFFER. ENCE operations require that the relations on which they are applied be union compatible?

Short Answer

Step by step solution

Define Union Compatibility

Explain need of Union compatibility for UNION operation

Explain need of Union compatibility for INTERSECTION operation

Explain need of Union compatibility for DIFFERENCE operation

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