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Describe the Composite Key
Composite Key: Sometimes one key is not enough to uniquely recognize a row. E.g. in a single class Roll is enough to search a student, but in the whole school, merely searching by the Roll is not enough, because there could be 10 classes in the school and every one of them may have a certain roll no 5. To uniquely recognize the student we have to say something like "class VII, roll no 5". So, a combination of two or more attributes is combined to make a unique combination of values, such as Class + Roll.
Consider the following database schema: STAFF(StaffNo, fName, lName, Position, sex, dob, branchNo) BRANCH(BranchNo, Street, City) Assume the following for the above database
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.
Can a domain, assigned to a data element be changed? Yes. We can do so by just overwriting the entry in the field domain.
Now that she understands more about the benefits of databases, the play-scheme manager would like to extend the play-scheme database to include data for schools and instructors as
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What is data independence? Data Independence: Techniques which permit data to be changed without affecting the applications in which procedure it. There are two types of data
Q. What is relational algebra and calculus? Explain the relational algebra operators :- Selection and predicate, set operation, joins and division. Sol. Relational Algebra
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