Relational Algebra

Consists of a set of operations on the universe

U

of finite relations over an underlying universe of values D of a database instance DB

Constants
- $R_{i}$ - Relation name
  - One for each relation name in a signature $p$
- $c_{i}$ - Constant
  - One for each constant in $D$
Unary Operations
- $σ$ - Selection
  - Removes rows
- $π$ - Duplicate preserving projection
  - Removes columns
- elim - Duplicate elimination
Binary Operations
- $\times$ - Cross product
- $\cup$ - Multiset union
- $-$ - Multiset difference

Query