Consider the query execution plans in Figure 11.3. Show how each of these plans can be enhanced by pushing the projection operator past the join without altering the strategies used for computing the join.
What will be an ideal response?
In plans (a) and (c), projection cannot be pushed to Teaching, because this would obliterate the index on ProfId and prevent the use of the indexed join strategies.
In case (a), we must preserve Id, DeptId, and Name for the subsequent operations. Since these are all the attributes in Professor, there is nothing to push. In case (c), we can push ?Id,Name.
In case (b), we can push ?Id,Name to Professor and ?ProfId to Teaching.
In case (d), we cannot push anything to Professor for the same reason as in case (a), but we can push ?ProfId to Teaching.
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Which of the following statements is false?
a. Variables declared in the body of a particular method are local variables and can be used only in that method. b. A method’s parameters are local variables of the method. c. Every method’s body is delimited by left and right braces ({ and }). d. Keyword null indicates that a method will perform a task but will not return any information.
Consider the schema with the attribute set ABCDEFH and the FDs. Prove that the decomposition (AD; A ? D ), (CE; C ? E ), (FA ; F ? A), (EF ; E ? F ), (BHE; BH ? E) is not lossless by providing a concrete relation instance over ABCDEFH that exhibits the loss of information when projected on this schema.
What will be an ideal response?
A loop for which the number of iterations is predetermined is called a(n) ____ loop, or counted loop.
A. infinite B. definite C. optimal D. defined
A conditional expression is an expression that results in a true or false value.
Answer the following statement true (T) or false (F)