SQL query Beginner's Guide reading notes (i) relational database and SQL introduction

Part i:relational Databases and SQL

Chapter2, ensuring Your Database Structureis sound.

Database Design Guidelines

What is a relational database

RDBMS (A relational database management systems) relational database

Tables

Tables is the mainstructures in the database. Each table always represents a

Single, Specificsubject.

Fields

A field is thesmallest structure in the database, and it represents a characteristic

of the subject ofthe table to which it belongs.

Records

A record Representsa unique instance of the subject of a table.

Keys

Keysare Special fields that play very specific roles within a table. eg.

• Primary key

• FOREIGN key

The primary key role is to ensure the uniqueness of the data record, that is, the primary key constraints to ensure that all data records in a database table are different individuals, for example: The ID number can guarantee a person in the mainland is a separate individual (not counted), That is, an identity card number can not identify two persons or two identification number identification of a person. So the primary key is analyzed from the existing data, not the designer arbitrarily added.

Relationships

• One-to-one

• One-to-many

• Many-to-many

SQL query Beginner's Guide reading notes (i) relational database and SQL introduction