SQL was created to support relational database management systems (RDBMSs). It was not created just for SQL Server. SQL, or as it is typically pronounced sequel, has been the de facto standard for working with relational databases for nearly 50 years. The structure and understanding of this language have been established as a standard in both ANSI and ISO.

While the language has a standard and well-established set of syntax rules and capabilities, it has been implemented in many ways throughout the years by various RDBMS vendors. Microsoft implemented Transact-SQL (T-SQL) in SQL Server and has continued to use it as the primary SQL version, used in the various Azure SQL Database implementations.

While the focus of our book is primarily around retrieving data from databases efficiently, SQL is not limited to just data retrieval. SQL can be used to manipulate the database structure, manipulate data, and retrieve data. SQL can also be used to issue commands to the underlying database system depending on what the language supports.

As we move into the modern data estates, relational data is not the only data within the environment. We are seeing more document-style databases and other non-relational datasets used in common practice. What is interesting about this is that there is always a push to get back to SQL-supported datasets. The tabular nature of the data returned by SQL is the easiest data to consume in numerous tools available in the marketplace today and is easy for users to understand. Languages and document sets such as JSON are highly flexible and support a less structured version of data. However, those sets often must be converted to a tabular format to be easily consumed by various tools and understood by the users consuming that data. Think of it like JSON a machine and developer-friendly data storage format, but tabular formats used by SQL make it easy for you to understand what is in it.

As we move into some of these modern scenarios and even in some older scenarios such as MDX, we find the SELECT... FROM... WHERE format of the SQL language has been implemented to make it easier to work with data. As a developer, it is important for you to understand the best formats and most efficient methods of writing these queries to get the results you need. A lot of these efficiencies are true for whatever database system you work in. This book will focus on working with SQL Server and T-SQL in particular; however, many of the principles will apply across all relational systems.