Relational Databases
A vast majority of modern databases are still relational databases. The entire database system is referred to as a relational database management system (RDBMS). RDBMSs group related data into table structures. Each stored record is a row in the table. Columns in the table define what is stored in each table. A column has strict rules that lay down what is allowed in each row’s entry for that column. For example, some columns only allow integers, and some must be filled with a value while some can be left blank. The ‘relational’ part of a RDBMS comes from the relationships between the tables. Tables can, and usually do, have keys. Each key is a unique identifier for the record in a table. This can be as complex as multiple columns designated as a key, or as simple as a column holding a unique number. Keys can be referenced in other tables. These references make up relationships.
SQL (pronounced ‘es-que-el’) is the standard language...