What Are Query Languages?

Query languages can be used to retrieve and manipulate data stored in databases and information systems, for example requesting employee or medical records, or recording the sale of a product.

Type "Query language" in wikipedia.org and they have a nice listing of querying languages and their uses.

One example of a database engine and querying language is the open source MySQL, popular in web applications. Say I had a table in a database that contained employee details (ID, name, email address, date of hire, etc.). If I wanted to retrieve a list of the employee records that included only the employee ID and name, and only employees hired before January 1 2008, the database query might look like:

Select employee_id, employee_name from t_employees where date_hired < 2008-01-01, order by employee_name;

You can also use the language to request changes to be made to the information repository. For example, a new employee was hired:

Insert into t_employees (employee_name, date_hired) VALUES
('Jane Doe', '2009-05-01');