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How does a query tree represent a relational algebra expression? Discuss any three rules for query optimisation, giving example as to when should each rule be applied.
Ans: A query tree is a tree structure which refers to a relational algebra expression. It denotes the input relations as leaf nodes of the tree, and denotes the relational algebra operations as internal nodes. An execution of the query tree contains executing an internal node operation while its operands are available and after that replacing that internal node by the relation which results from executing the operation. The execution terminates while the root node is executed and generates the result relation for the query. For instance, the query tree for the relational algebra expression
∏E_No =(σp_No = 'DB2003' (Assigned_To) :
The three rules for query optimization are like this:
∏1(∏2(......∏n ( R))) ≡ ∏1(R )
∏A1, A2,......An (σC (R ) ≡ σC (∏A1, A2, ......An (R ))..... ))
σC1 AND C2 AND ....AND Cn (R ) ≡ σC1 (σC2(....(σCn (R ))....))
management information system based on functional organisation
Change the city of First Bank Corporation to ‘New Delhi' UPDATE COMPANY SET CITY = ‘New Delhi' WHERE COMPANY_NAME = ‘First Bank Corporation';
Hardware failure : Hardware failures are the failures when some disk or hardware chip fails. This may result in loss of data. One such trouble can be that a disk gets damaged and
1. Item based services will be charged fixed prices, and time-based will be charged variably depending on time. Such as per hour. Item-based: Fixed, pedicure, waxing, threading, fa
The Database Approach In order to overcome the limits of a file system, a new approach was needed. Hence a database approach emerged. A database is a persistent collection of
Consider the following relations: S (S#, SNAME, STATUS, CITY) SP (S#, P#, QTY) P (P#, PNAME, COLOR, WEIGHT, CITY) Give an expression within SQL for each of queries b
what should be included in this???
The objectives of this assignment are: - to develop skills in the design of database driven applications - to develop skills in applying SQL to implement the relational and
explain equi-join using illustration
What is meant by computing the closure of a set of functional dependency? The closure of F denoted by F + is the set of functional dependencies logically implied by F.
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