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A database is a set of data. But, is the data kept in a database trustworthy? To answer that query we must first answer the question. What is integrity?
Integrity simply means to keep the consistency of data. Therefore, integrity constraints in a database make sure that changes made to the database by authorised users do not compromise data consistency. Therefore, integrity constraints do not permit damage to the database.
There are primarily two integrity constraints: the referential integrity constraint and the entity integrity constraint. In order to describe these two, let us first describe the term Key with respect to a Database Management System.
Attribute Preservation This is a easy and obvious necessity that includes preserving all the attributes that were there in the relation that is being decomposed.
Having Clause with sub queries: First we have to recollect the GROUP BYclause. The following query searches the minimum salary in every department. SELECT DEPTNO, MIN (SAL)
Cardinality of Relationship One-to-One Only one entity of the first set is linked to only one entity of the second set. E.g. A teacher teaches a student. Only one teacher
Define multivalued dependency. What do understand by trivial multivalued dependency? Ans: A multivalued dependency is a full constraint among two sets of attributes in a rela
#questiRegional Gardens has many nurseries, including Wagga Wagga, Bathurst, Albury, Orange, and Dubbo. Each nursery is known by its campus code, eg WW, B, A, O and D respectively.
First Normal Form and second normal form First Normal Form (1NF) A relation is said to be in 1NF if it having no non-atomic values and each row can give a unique combinat
Explain the θ-join and equijoin Refer tables Car and Boat which list models of cars and boats and their relevant prices. Assume a customer wants to buy a car and a boat, but sh
A model in database system mostly defines the organisation of data or structure and a set of operations on that data. Relational model is a easy model in which database is represen
Consider an information system designed for an online company which provides IT products and services These include desktops, laptops, networking products, IT books, parts, and
We will explain here an example database application having COLLEGE database and use it in showing several E-R modelling concepts. College database remains track of faculty, Stu
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