Data Definition (DDL)

In SQL the terms table, row and column are synonyms for relation, tuple and attribute. To create a new relation scheme in the database we start with the create table-command. Together with the creation we must provide the relations attributes and their domains (e.g. number, char or date). Additional we can define other constraints, checks and keys etc. The keyword NOT NULL tells the system that this attribute cannot be empty. Primary keys are declared using a special "table constraint"-clause.

This example shows how a new table is created in SQL. In the intermediate lesson we take a closer look at all the SQL statements. For the moment you don't have to understand these statements in detail.