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In a relation, tuples are not inserted in any definite order. Ordering of tuples is not defined as a part of a relation definition. Though, records may be structured later according to some attribute value in the storage systems. For instance, records in PERSON table may be structured according to PERSON_ID. Such organisation or data depends on the requirement of the underlying database application. Though, for the purpose of display we may get them displayed in the sorted order of age. The following table is sorted by age. It is also worth states here that relational model does not permit duplicate tuples
PERSON
PERSON_ID NAME AGE ADDRESS
2 Sharad Gupta 33 Pocket 2, Mayur Vihar.
1 Sanjay Prasad 35 b-4,Modi Nagar
3 Vibhu Datt 36 c-2, New Delhi
Super Keys, Candidate Keys and Primary Keys for the Relations
As discussed in the last section ordering of relations does not matter and all tuples in a relation are unique. Though, can we uniquely recognize a tuple in a relation? Let us talk about the concepts of keys that are primarily used for the purpose as above.
Physical Database Design Issues The database design includes the process of logical design with the use of E-R diagram, normalisation, etc., followed by the physical design.
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Consider entity type Employee with attributes empNumber (this is unique), empName, and the year when he/she was hired. An employee can either be a technical employee, a marketing e
What are the Objectives of object design After going through this unit, you could be able to: explain steps of object design; discuss algorithms that reduce costs;
#explain five disadvantages of a dbms..
There are many simple and complex approaches to implement. These reports are based on some views or certain query. The following number of reports can be built. 1. The averag
Explain the Attribute inheritance Ans: Throughout the rendering of the objects in a view, attribute sets of objects higher in the view hierarchy are inherited via objects below
what is union compatable?
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Compare the Nested-loop join and block-nested loop join Ans: Nested loop join - It is costly as worst case cost, no. of block accesses needed is n r * b s + b r where b
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