SQL is a domain-specific language used in programming and designed for managing data held in a relational database management system (RDBMS), or for stream processing in a relational data stream management system (RDSMS). It is particularly useful in handling structured data, i.e. data incorporating relations among entities and variables.
This book will teach you the basics of SQL and database operations. Since SQL is a language used to manage databases, you have to familiarize yourself with its basics and nuances. Don't worry if you have never used SQL before: this book will turn you from a beginner to an efficient SQL-user.