What is a query in a database?

A query in a database is a request for data or information from a database table or combination of tables.

In more detail, a query is a way to retrieve information from a database that matches specific criteria. This is done using a special syntax known as Structured Query Language (SQL). SQL is a standard language for managing and manipulating databases. It can be used to search the database, update or delete records, create new databases, tables and views, and set permissions on tables, procedures, and views.

A query can be as simple as asking for all records from a single table, or it can be complex and involve data from multiple tables, applying filters, and sorting the results. For example, you might want to find all customers from a certain city, or all orders placed in the last week. These requests are written as queries in SQL.

Queries are essential for managing databases and manipulating the data within them. They allow users to interact with the data, whether that's retrieving specific information, updating records, or creating new data. They are a fundamental part of any database management system (DBMS), which is software that interacts with the user, other applications, and the database itself to capture and analyse data.

In addition to SQL, there are other query languages such as XQuery for XML databases, and SPARQL for RDF databases. However, SQL is the most widely used and recognised. It's important to note that while the basic syntax of SQL is standard, different DBMSs may have their own additional proprietary extensions that are usually only used on their system.

In conclusion, a query is a crucial tool in database management, allowing for the retrieval, manipulation, and management of data stored within a database. Understanding how to write and use queries is a key skill in database administration and development.