Introduction to SQL

SQL is a declarative language for storing, manipulating, and querying data stored in relational databases, also called relational database management systems (RDBMSes). A relational database contains data in tables, which in turn contain rows and columns. In the real world, entities have relationships among themselves, and a relational database tries to mimic these real-world relationships as relationships between tables. Thus, in relational databases, individual tables contain data related to individual entities, and these tables might be related.

SQL is a declarative programming language that helps you specify which rows and columns you want to retrieve from a given table and specify constraints to filter out any data. An RDBMS contains a query optimizer that turns a SQL declaration into a query plan and executes it on the database engine. The query plan is finally translated into an execution plan for the database engine to read table rows and columns into...