Relational Database

A relational database is a database model that stores data in tables. The vast majority of databases used in modern applications are relational, so the terms "database" and "relational database" are often used synonymously. Likewise, most database management systems (DBMSes) are relational database management systems (RDBMSes). Other database models include flat file and hierarchical databases, though these are rarely used.

Each table in a relational database contains rows (records) and columns (fields). In computer science terminology, rows are sometimes called "tuples," columns may be referred to as "attributes," and the tables themselves may be called "relations." A table can be visualized as a matrix of rows and columns, where each intersection of a row and column contains a specific value. It is "relational" since all records share the same fields.

Database tables often include a primary key, which provides a unique identifier for each row within the table. The key may be assigned to a column (which requires a unique value each row), or it may be comprised of multiple columns that together form a unique combination of values. Either way, a primary key provides an efficient way of indexing data and can be used to share values between tables within a database. For example, the value of a primary key from one table can be assigned to a field in a row of another table. Values imported from other tables are called foreign keys.

The standard way to access data from a relational database is through an SQL (Structured Query Language) query. SQL queries can be used to create, modify, and delete tables, as well as select, insert, and delete data from existing tables.