Learn: DBMS exam 1 refresher

Superkey

An attribute or set of attributes that uniquely identifies a tuple.

Candidate Key

A minimal superkey; no proper subset of it is also a superkey.

Primary Key

The candidate key selected to uniquely identify tuples in a relation.

Foreign Key

An attribute or set of attributes whose values reference the primary key of another table.

Selection (σ)

Returns only the tuples/rows that satisfy a specified condition or predicate.

Projection (π)

Returns specified attributes/columns and eliminates duplicate resulting tuples.

Union (∪)

Returns tuples in R, S, or both; duplicates are eliminated.

Set Difference (−)

Returns tuples that are in R but not in S.

Intersection (∩)

Returns tuples that occur in both R and S.

Cartesian Product (×)

Combines every tuple of one relation with every tuple of another relation.

Join (⋈)

Combines tuples from two relations according to a join condition using compatible join attributes.

Join Condition

The condition specifying how tuples from two relations are matched during a join.

Join Attribute

An attribute used to join two relations; the participating attributes have the same domain.

Natural Join

A join over common same-named attributes that removes the duplicate occurrence of the common join attribute.

Join Selectivity

The number of records in the join result divided by the relevant number of records used for comparison.