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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.
What is the difference among a database schema and a database state? The collection of information stored in database at particular moment in time is known as database state a
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atient(PNumber, Name, NHS_no, Amount_due, DNO, Doctor, Medical_Treatment), relation of schema Staff(StaffNum, Name, DNO, Task) and relation of schema Dept(DNO, Name, Location, Dire
Consider a systems development project with the following data Activity Duration (weeks) Precedence Relationship 1. Software design
Database Recovery And Security Introduction In this part we will introduce two main issues relating to database management systems. A computer system suffers from dissi
Aggregate functions Some of these functions are min, count, max, and avg. These functions help in getting consolidated information from a set of tuples. Example:
Consider the following relational database: STUDENT (name, student#, class, major) COURSE (course name, course#, credit hours, department) SECTION (section identifier, course#, sem
Multiple-mode locks : It offers two locks: exclusive locks and shared locks. But why do we require these two locks? There are a lot of transactions in the database system that neve
What is Foreign Key Foreign Key: Sometimes we may have to work with an attribute that does not have a primary key of its own. To recognize its rows, we have to use the primar
Define NULL value NULL value NULL means something is unknown. It does NOT mean null (the digit 0). Null is as well employed as attribute value for a particular entity in which
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