SQL for Data Scientists

CHAPTER 2The SELECT Statement

Before we can discuss designing analytical datasets, you first need to understand the syntax of Structured Query Language (SQL), so the next several chapters will cover SQL basics. Throughout the book, you will see many variations on the themes introduced here, combining these basic concepts with increasing complexity, because even the most complex SQL queries boil down to the same basic concepts.

The SELECT Statement

The majority of the queries in this book will be SELECT statements. A SELECT statement is SQL code that retrieves data from the database. When used in combination with other SQL keywords, SELECT can be used to view data from a set of columns in a database table, combine data from multiple tables, filter the results, perform calculations, and more.

NOTE

You'll often see the word SELECT capitalized in SQL code, and I chose to follow that formatting standard in this book, because SELECT is a reserved SQL keyword, meaning it is a special instructional word that the code interpreter uses to execute your query. Capitalizing it visually differentiates the keyword from other text in your query, such as field names.

The Fundamental Syntax Structure of a SELECT Query

SQL SELECT queries follow this basic syntax, though most of the clauses are optional:

• SELECT [columns to return]
• FROM [schema.table]
• WHERE [conditional filter statements]
• GROUP BY [columns to group on]
• HAVING [conditional filter statements that are run after grouping] ...