E.F. Codd conceived the relational database in 1970. He worked at IBM and published “Codd’s 12 Rules.” A small start-up company released the first RDBMS and called it ORACLE. Then IBM published their version as SEQUEL-XRM and it later became DB2. A Relational DataBase Management System (RDBMS) is a database divided into logical units called tables, where the data in the two-dimensional tables are related to one another within the database. These tables are largely independent, which gives relational databases their flexibility. You can add, change, or delete data in one table without affecting other tables, provided that the changed table is not a parent of any other table. (Parent-child tables are discussed later.)
SQL operators are used to select rows or columns of data from the table, producing a new, temporary result table. This language differs considerably from previous DBMS languages, because it returns one or many rows (or records) with each query. We will show you later how to handle the individual rows. Next we will see how easy SQL is to use!