Relational algebra operators - Database

Q.  Which is not the relational algebra operator?
- Published on 19 Oct 15

a. Set difference
b. Cartesian product
c. Rename
d. Join

ANSWER: Set difference
 

    Discussion

  • Nirja Shah   -Posted on 30 Oct 15
    Set difference
    - It is the difference (or simply difference) between A and B (in that order) is the set of all elements of A that are not in B.

    Cartesian Product (X)
    - It combines information of two different relations into one.
    Notation - r X s
    - Where r and s are relations and their output will be defined as -
    r X s = { q t | q ∈ r and t ∈ s}

    Rename Operation (ρ)
    - This operation are results of relational algebra which are also relations but without any name.
    - It allows us to rename the output relation. 'rename' operation is denoted with small Greek letter rho ρ.
    Notation - ρ x (E)
    - Where the result of expression E is saved with name of x.
    - Additional operations are -
    1. Set intersection
    2. Assignment
    3. Natural join

    Join
    - It combines records from two or more tables in a relational database.
    - They create a set that can be saved as a table or used as it is.
    - A JOIN is a means for combining fields from two tables (or more) by using values common to each.

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