A query represents the retrieval of information from a database. Requesting a query is not a difficult job, but it involves writing the query using a pre-defined code. In this way, the database can understand the instruction and can display the information requested.
A query refers to the action of retrieving data from a database and formatting it into a human-readable form.
A database query is classified into action queries or select queries.
Retrieving data can be done using a select query and other operations on the data such as updating, inserting or deleting can be done using an action query.
How can a query be requested?
There are three general methods for posing queries: choosing parameters from a list of parameters (this is the least flexible way, but the easier way for the beginners because the menus guide them), specifying the fields and values that define the query (query by example) and using a query language (the most powerful method, but also the most difficult because the person who requires the query has to know a query language). SQL (Structured Query Language) is the most well-known and widely-used query language. While SQL is the most popular language, it is not the only one. Other languages are, for example, Datalog, DMX, AQL.
How can a query be used?
Queries can be used in different ways and can achieve many tasks.
Firstly, queries are used to find specific data by filtering specific criteria. Also, queries can count or sum up data, as well as automate data management tasks. Other queries include parameter, totals, crosstab, attach, update and delete.
For example, a parameter query runs variations of a particular query, that induce a user to insert a field value, and then it uses that value to establish the parameters, while totals queries allow users to group and sum up data.