A query is a specific request for information from a database. In robust database systems in particular, queries make it easier to perceive trends at a high level or make edits to data in large quantities. Queries enable users to locate records that meet certain criteria, make complex calculations, apply intricate operations to a large data set, and automate functions that are essential for data management. They also make it possible to consolidate data into digestible pieces of information for reporting purposes.
Types of queries
Regardless of the database or query language used, there are two primary types of queries that can be used for different goals:
- Select queries return information from one or more tables. While this is the most basic type of query, select queries can be used to specify how many results are returned, the order in which they appear, the source(s) used, and the parameters for a record to be included.
- Action queries perform a command on the data that has been retrieved, such as delete, alter, create, or update. This query allows a user to modify a large number of records in bulk instead of one at a time.
Numerous query languages exist today. The most prevalent language is Structured Query Language (SQL), which is not to be confused with Microsoft SQL Server or the NewSQL class of databases. SQL is compatible with any database and serves as the foundation for many query language adaptations, so it has become a must-learn for most data scientists. Other languages include XQuery for XML documents, SPARQL for the Resource Description Framework (RDF) data model, and others.