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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.
Describes the several relationship constraints through giving suitable example? Constraints on relationships: There are two kinds of constraints on relationships. 1) Mapping
Explain degree of relation? Degree of a Relation - The degree or arity of a relation is the number of attributes n of its relation schema.
Scenario 1: Power goes out after the first instruction. What happens?
What is trigger? Triggers are statements that are executed automatically by the system as the side effect of a modification to the database.
It can be easily defined as: The database must not have any unmatched foreign key values. The term "unmatched foreign key value" means a foreign key value for which there doe
Replicating Data One approach that may support efficient access to dissimilar applications as above may be to give access to every of the applications from dissimilar replicate
Security: In a centralised system, access to the data can be simply controlled. Though, in a distributed DBMS not only does access to replicated data have to be controlled in many
What is persistency? Persistency ensures which data is stored and that after the object is no longer available (program stops running) the data will be available to other users
Construct an ER diagram for a hospital along with a set of patients and a set of medical doctors Associate with every patient a log of the several tests and examinations conducted.
Describe substring comparison in SQL. For the relation Person (name, address), write a SQL query that retrieves the names of people whose name starts along with ‘A' and address co
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