# RDBMS¶

B+ trees

• 1-1
• 1-many
• many-many

### Constraints¶

• cardinality ratio / degree
• participation constraints

### Keys¶

• candidate - unique, nC(floor(n/2))
• super - cadidate + X
• alternate
• foreign

### Relational algebra¶

Operation(Symbols) Purpose
Select(σ) subset of tuples given condition
Projection(π) The projection eliminates all attributes of the input relation but those mentioned in the projection list.
Union Operation(∪) all in A or/and in B
Set Difference(-) A not B
Intersection(∩) both in A and B
Cartesian Product(X) merge columns of 2 tables
Inner Join Inner join, includes only those tuples that satisfy the matching criteria.
Theta Join(θ) The general case of JOIN operation is called a Theta join. It is denoted by symbol θ.
EQUI Join When a theta join uses only equivalence condition, it becomes a equi join.
Natural Join(⋈) Natural join can only be performed if there is a common attribute (column) between the relations.
Outer Join In an outer join, along with tuples that satisfy the matching criteria.
Left Outer Join In the left outer join, operation allows keeping all tuple in the left relation.
Right Outer join In the right outer join, operation allows keeping all tuple in the right relation.
Full Outer Join In a full outer join, all tuples from both relations are included in the result irrespective of the matching condition.