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What is meant by heuristic optimisation?Discuss the major heuristics that are applied during query optimisation.
Ans: In heuristic opimization, heuristics are employed to decrease the cost of optimization in place of analyzing the number of dissimilar plans to find out the optimal plan. For instance A analyzing optimizer would make use of the rule 'perform selection operation as early as possible' without finding out whether the cost is decreased by this transformation. Heuristics approach generally assists to reduce the cost but not always. The heuristics which are applied during query optimization are:
a) Pushes the selection and projection operations down the query tree
b) Left-deep join trees- convenient for pipelined evaluation
c) Non- left-deep join trees
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A constraint named less_than_20 was defined on the field date_of_birth of table student. Delete this constraint. ALTER TABLE student DROP CONSTRAINT less_than_20;
Explain pipelining. Ans: In order to describe pipelining in simple terms, think of it as breaking down processor functions into smaller and smaller parts. For instance,
Which two tools are used to administer users for Active Directory?
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explain participation constraints with examples
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