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Classify the following operations in relational algebra into unary and binary operations:(1) UNION(2) SELECT(3) SET DIFFERENCE(4) PROJECT(b) Explain about SELECT, INTERSECTION and SET DIFFERENCE operations with example. |
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Answer» (a) Unary Binary (2) SELECT (1) UNION (4) PROJECT (3) SET DIFFERENCE (b) SELECT operation SELECT operation is used to select tuples in a relation that satisfy a selection condition. Greek letter cr (sigma) is used to denote the operation. Syntax, σCondition(relation) eg. σSalary<100000(EMPLOYEE)-selects tuple whose salary is less than 10000 from EMPLOYEE relation. Intersection operation This operation returns a relation consisting of all the tuples appearing in both of the specified relations. It is denoted by n. It can takes place only on compatible relations, e.g. FOOTBALL ∩ CRICKET returns the players who are in both football and cricket teams. Set difference operation (-) All tuples appearing in the first relation and not in the second |
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