Database-MySQL [3i Infotech Placement]: Sample Questions 120 - 121 of 162

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Question 120

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Describe in Detail

Essay▾

What is Relational Algebra?

Explanation

Structure of Relational Algebra in DBMS
  • The relational algebra is a theoretical procedural query language which takes instance of relations and does operations that work on one or more relations to describe another relation without altering the original relation.
  • So, both the operands and the outputs are relations, and so the output from one operation can turn into the input to another operation which allows expressions to be nested in the relational algebra.
  • The relational algebra is a relation-at-a-time (or set) language where all tuples are controlled in one statement without the use of loop.
  • There are several variations of syntax for relational algebra commands and you use a common symbolic notation for the commands and present it informally.
  • The primary operations of relational algebra are as follows:
    • Select
    • Project
    • Union
    • Set different
    • Cartesian product
    • Rename

Question 121

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Describe in Detail

Essay▾

What is degree of a Relation?

Explanation

Degree of a Relationship with Types
  • The degree of a relation is the number of attributes n of its relational schema.
  • An example of a relational schema for a relation of degree seven, which describes university students, is the following:
    • STUDENTS (Name, Ssn, Home_phone, Address, Office_phone, Age, Gpa) ″

    The main three relational degrees are:

  • Ornary (one relational connection)
  • Binary (two relational connection)
  • Ternary (three relational connection)

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