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Question:(a) The objective of query optimization is to choose the most efficient strategy for implementing a given relational query, thereby improving the system performance. One of the stages of query optimization is to convert the internal form into equivalent and more efficient canonical form, using well-defined transformation rules. Two rules of the transformation rules is given below:Rule 1 - Transform a sequence of restrictions against a given relation into a single (ANDed) restriction.Rule 2 - Transform a restriction of a projection into a projection of a restriction.(i) Explain what is meant by each of the above rules.(ii) Using the relational schema given in Appendix, provide example of each of the above rules.(b) Refer to the relational schema given in Appendix.Assuming that: The Employee relation contains 1000 records among which 300 employee are assigned to departments located in the United States.- The Department relation contains 30 records among which 20 departments are located in United States- The Location relation contains 20 records among which 5 are situated in the United States.(i) Express the following query in SQL:"find the employee Last names and the department names who are working in United States (Location.country_id = US)(ii) Choose two possible methods to evaluate the query, and use the relational algebra to formulate clearly all the steps required in the evaluation. For each method, calculate the number of tuples for all the intermediate relations (namely, size of the intermediate relations) required for each step.
Loop Labels Like the PL/SQL blocks, loops can also be labeled. The label, an undeclared identifier enclosed by double angle brackets, should appear at the beginning of the LOOP
Boolean Values Only the values TRUE, FALSE, & NULL can be assigned to a Boolean variable. For illustration, given the declaration DECLARE done BOOLEAN; the following statements
set serveroutput on declare a number(5); b number(5); c number(5); begin a:=&a; b:=&b; c:=a/b; dbms_output.put_line(c); exception when zero_d
Assignment Statement: The assignment statement sets the present value of the variable, parameter, field, or element. The statement consists of an assignment target followed by
Use the NOCOPY Compiler Hint By default, the OUT and IN OUT parameters are passed by the value i.e. the value of an IN OUT actual parameter is copied into the corresponding fo
Using %TYPE The %TYPE attribute gives the datatype of a variable or the database column. In the example below, the %TYPE gives the datatype of a variable: credit REAL(7,2); debi
Order of Evaluation When you do not use the parentheses to specify the order of evaluation, the operator precedence determine the order. Now compare the expressions below: NOT
Literals A literal is an explicit numeric, string, character, or Boolean value not represented by an identifier. Numeric literal 147 and the Boolean literal FALSE are some of
Extension and AND in SQL The theory book gives the following simple example of relational extension in Tutorial D: EXTEND IS_CALLED ADD ( FirstLetter ( Name ) AS Initial )
IN Operator The operator IN tests the set membership. This means "equal to any member of." The set may have nulls, but they are ignored. For illustration, the statement below do
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