DBMS
Relational Algebra: Selection, Projection and Rename
The three unary operators. Selection picks rows, projection picks columns and removes duplicates, and rename makes an expression reusable. Together th...
Relational Algebra
Selection, projection, set operations, Cartesian product, rename, joins, division and building algebra expressions.
6 notes
Notes
DBMS
Set Operations in Relational Algebra
Union, intersection and difference come straight from set theory, but they require union compatibility. Cartesian product combines every pair and is t...
DBMS
Join Operations in Relational Algebra
Theta join, equi join and natural join, all defined as a selection over a Cartesian product. The natural join joins on every common attribute and remo...
DBMS
Outer Joins, Semi Join and Anti Join
Inner joins discard unmatched tuples. Outer joins keep them and pad with nulls. Semi join keeps only the left tuples that matched, and anti join keeps...
DBMS
The Division Operator
Division answers questions containing the word every. It is the hardest operator to recognise and the easiest to verify, and it can always be rewritte...
DBMS
Building Relational Algebra Expressions
How to turn an English question into an algebra expression, read an expression tree, and apply the equivalence rules an optimiser uses to make the sam...