An Introduction to SQL

Structured Query Language (SQL) is a programming language used to manage relational databases. Databases store information and then allow this information to be accessed and manipulated.

Relational Databases

A relational database organizes information into tables. The structure of a relational database is similar to that of an Excel spreadsheet. The tables in a database can be thought of like individual sheets within one big Excel file, which would be the database. Each table contains data which is organized into columns and rows. Each column holds a particular type of value.

For example, if we had a table of information about pets, it could have columns for a pet’s name, species, and age. The table would also have an id column. This is a very important column that should appear in every table. Each row in a table has an id which identifies that piece of information and can be used to extract data from this row for use.

Writing SQL Queries

SQL is used by writing declarative statements, often referred to as queries. There are many SQL clauses that are used to write SQL statements. Some of the most common clauses are as follows.

SELECT — extracts data from a database