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Illustrate the statement 'Projection operation distributes over the union operation'. Give an example.
Ans: ΠL(E1 ∪ E2) = (ΠL(E1)) ∪ (ΠL(E2))
This says that result acquired by projecting on an attribute set A, after taking union of two relations is similar as union of two relations each of which is a projection of original relations on A.
Probelm: (a) A distributed database (DDB) is a collection of multiple, logically interrelated databases which are physically distributed over a computer network" (i) Give a
Multiple column Queries: Syntax: SELECT COLUMN1, COL2,...... FROM TABLE WHERE (COLUMN1, COL2, ...) IN (SELECT COLUMN1, COL2,.... FROM TABLE WHERE );
what is specialization?
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Saving Derived Attributes to Avoid Re-computation As discussed, "redundancy means duplication of exact data". But, if multiple copies of same data are present in the system,
Primary Key The primary key is the candidate key that is selected by the database designer as the principal denotes of identifying entities within an entity set. The left candi
Explain What is Relation? A database relation is a predefined row or column format for storing information in a relational database. Relations are equal to tables.
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