Book Image

The SQL Workshop

By : Frank Solomon, Prashanth Jayaram, Awni Al Saqqa
Book Image

The SQL Workshop

By: Frank Solomon, Prashanth Jayaram, Awni Al Saqqa

Overview of this book

Many software applications are backed by powerful relational database systems, meaning that the skills to be able to maintain a SQL database and reliably retrieve data are in high demand. With its simple syntax and effective data manipulation capabilities, SQL enables you to manage relational databases with ease. The SQL Workshop will help you progress from basic to advanced-level SQL queries in order to create and manage databases successfully. This Workshop begins with an introduction to basic CRUD commands and gives you an overview of the different data types in SQL. You'll use commands for narrowing down the search results within a database and learn about data retrieval from single and multiple tables in a single query. As you advance, you'll use aggregate functions to perform calculations on a set of values, and implement process automation using stored procedures, functions, and triggers. Finally, you'll secure your database against potential threats and use access control to keep your data safe. Throughout this Workshop, you'll use your skills on a realistic database for an online shop, preparing you for solving data problems in the real world. By the end of this book, you'll have built the knowledge, skills and confidence to creatively solve real-world data problems with SQL.
Table of Contents (13 chapters)

Primary Key Constraints

A primary key constraint on a column instructs the database engine to keep the entries in a column unique. For example, if we were to create a table with information about all the human beings on Earth, we could use the tongue print of human beings as unique identification. If tongue prints were in a column, it would be the primary key.

It is possible to have a duplicate tongue print; however, it is rare. In such a case, you could create a primary key across multiple columns. Therefore, you could combine the tongue print, fingerprint, and the retinal signature to make a primary key. In such a case, the combination of these values in these columns should be unique across the table. In other words, there may be a duplicate tongue print, a duplicate fingerprint, and a duplicate retinal signature in the table—the database engine will allow that. However, there cannot be a duplicate combination of all three. Alternatively, there can be no two human beings...