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Relational algebra operators - Database
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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
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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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