IT 2101 Lecture Notes - Lecture 10: Cardinality, Foreign Key, Dbt Online Inc.

• School: KSU
• Department: Information Technology
• Course: IT 2101
• Professor: Robbie Hackworth

Document Summary

A relation is a two-dimensional table that has specific characteristics. The table dimensions consist of rows (also called records) and columns (also called attributes) Cells of the table hold a single value. All entities in a column are of the same kind (numbers, text or date but not mixed) The order of the columns is unimportant. The order of the rows is unimportant. A key is one (or more) columns of a table that is (are) used to identify a row. Keys are the key" to creating a relational database. A primary key is chosen to be the main key for the relation. If you know the value of the primary key, you will be able to uniquely identify a single row. No 2 rows in a table may have the same primary key. A table may be related to other tables. A student is enrolled in a class. To preserve relationships, you may need to create a foreign key.