Structured Query Language (SQL) is a standardized programming language that is used to manage relational databases and perform various operations on the data in them. Initially created in the 1970s, SQL is regularly used not only by database administrators, but also by developers writing data integration scripts and data analysts looking to set up and run analytical queries.
The term SQL is pronounced ess-kew-ell or sequel.
SQL is used for the following:
- modifying database table and index structures;
- adding, updating and deleting rows of data; and
- retrieving subsets of information from within relational database management systems (RDBMSes) -- this information can be used for transaction processing, analytics applications and other applications that require communicating with a relational database.
SQL queries and other operations take the form of commands written as statements and are aggregated into programs that enable users to add, modify or retrieve data from database tables.
A table is the most basic unit of a database and consists of rows and columns of data. A single table holds records, and each record is stored in a row of the table. Tables are the most used type of database objects, or structures that hold or reference data in a relational database. Other types of database objects include the following:
- Views are logical representations of data assembled from one or more database tables.
- Indexes are lookup tables that help speed up database lookup functions.
- Reports consist of data retrieved from one or more tables, usually a subset of that data that is selected based on search criteria.
Each column in a table corresponds to a category of data -- for example, customer name or address -- while each row contains a data value for the intersecting column.
Relational databases are relational because they are composed of tables that relate to each other. For example, a SQL database used for customer service can have one table for customer names and addresses and other tables that hold information about specific purchases, product codes and customer contacts. A table used to track customer contacts usually uses a unique customer identifier called a key or primary key to reference the customer's record in a separate table used to store customer data, such as name and contact information.
SQL became the de facto standard programming language for relational databases after they emerged in the late 1970s and early 1980s.
