Relational algebra operators - Database

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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