# Overview Each individual table represent an *entity* described by data (i.e., a User). The columns in the table are *attributes* of the entity (i.e., first name, favorite NFL team). Each row is a *record* that captures a different instance of an entity (i.e., a row for Ryan and a row for Bob). ![[Relational Databases 2024-09-16 10.44.25.excalidraw.svg]] ## Relationships [[Data Relationships]] between the tables, columns, and records are captured using *keys*. A **Primary Key** is a key on a table used to represent the unique rows (i.e., records of a table). Often, these are some sort of unique identifier, but for more details on creating a strong Primary Key, check out the resources in [[Data Modeling]], which is the act of designing how to represent your data in a database, application, or other components of a system. A table may also hold a **Foreign Key**, which is a column (i.e., attribute) that contains a reference to a key in another table. The relationships between one table's foreign key and another tables key is how data relationships are modeled and these keys can be used in [[Data Query and Processing Languages]] to join data from different tables together. This is done through [[SQL joins]]. ![[Relational Databases 2024-09-16 10.55.43.excalidraw.svg]] ### Modeling Relationships in a Relational Schema