tags: #sql

C

Candidate Keys (Minimal Superkey)

A candidate key is a key that can potentially be used as the primary key of the table. To be a candidate key, it must satisfy the following 2 conditions:

1. Unique - i.e., each value in the candidate key must be unique for every row in the table.
2. Minimalness - i.e., a superkey that cannot be further reduced without losing the property of being able to uniquely identify each row of data.

Catalog

A catalog is a named collection of schemas in an EQL environment.

Column ("field", "attribute")

A column corresponds to an attribute or property that describes an entity.

D

Database Management System (DBMS)

A DBMS is a software used to create and manage databases (e.g., MySQL, Oracle, PostgreSQL). It serves as an interface between an end-user and a database, enabling users to store, retrieve, and run queries on data.

E

Entity Integrity

Entity integrity ensures that:

1. Primary keys are unique (i.e., each row or record in a table represents a unique entity or object)
2. Each tuple MUST HAVE a valid PK (i.e., PK CANNOT be missing = NULL)

This means that no two records in a table can have the same primary key value, and no record can have a null value in its primary key field.

R

Row ("tuple")

A row is also referred to as a "tuple". This is a collection of related information about an entity.

Referential Integrity

Ensures that any foreign key value in a table must match a primary key value in another table, or be null, i.e., tuples in referencing relation R1 have attributes FK that references the PK attribute(s) of the referenced relation R2.

Referential integrity can be enforced through the use of foreign key constraints, which prevent the creation of orphaned records (i.e., records in a child table that reference non-existent records in the parent table) and the deletion of records that are referenced by other records in a different table.

S

Superkey

A superkey (SK) is a set of one or more attributes that can uniquely identify each tuple or row in a table, such that:

i.e., for all distinct tuples in r(R) - in a given relational state, no two tuples will have the same SK values.

T

Table ("relation")

A table is also referred to as a "relation" (i.e., a collection of records).