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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.
What is DAG? The class-subclass relationship is shown by a directed acyclic graph.eg: employees can be temporary or permanent. We might be create subclasses temporary \and perm
Consider the following frequency counts of some itemsets in a transaction database r : freq({A}, r) = 0.405 freq({B}, r) = 0.510 freq({C}, r) = 0.303 freq({A
Use again the GE Flight Quest Data and build on the work done for homework 1 and 2. The goal is to create a classification model which classifies flights into "on-time" (you can de
Law Associates is a large legal practice based in Sydney. You have been asked to design a data model for the practice based upon the following specification: The practice employs
How to create a table from existing table? Create table as e.g, To create a new table ‘N_emp' with employee names and their identification numbers only from employee ta
what is binary relationship
Which method of access uses key transformation? A Hash method of access uses key transformation.
Components of database manager The above functions are reached by the database manager. The major elements of a database manager are: Authorisation control: This mod
What is Data dictionary? A data dictionary is a reserved space in a database that is employed to store information about the database itself. A data dictionary may consist o
What is the full form of ODBC ? ODBC stands for Open Database Connectivity.
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