Whether you’re relatively new to writing SQL or you’ve been writing it for years, learning to write “good” SQL is a process that requires a strong knowledge foundation of core syntax and concepts. This chapter provides a review of the core concepts of the SQL language and its capabilities, along with descriptions of the common SQL commands with which you should already be familiar. For those of you who have worked with SQL previously and have a good grasp on the basics, this chapter will be a brief refresher to prepare you for the more detailed treatment of SQL we examine in later chapters. If you’re a new SQL user, you may want to read Beginning Oracle SQL first to make sure you’re comfortable with the basics. Either way, Chapter 1 “level sets” you with a whirlwind tour of the five core SQL statements and provides a quick review of the tool we’ll be using to execute SQL: SQL*Plus.