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What is a Query?

A query is a request for data or information from a database table or combination of tables. This data may be generated as results returned by SQL or as pictorials, graphs, or complex results, e.g., trend analyses from data-mining tools. One of several different query languages may be used to perform a range of simple to complex database queries. SQL, the most well-known and widely-used query language, is familiar to most database administrators (DBAs).

SQL represents one of the standard languages used for database management purposes, while MySQL, instead, is the software using that specific language. Although SQL is a fairly universal language, other commonly used ones include DMX, Datalog, and AQL.

A database query refers to the request of data or information from a database. It is used to records a table. It is performed using a database language that generates data of different types according to function. Several languages have been developed for different database engines and purposes, one such language is SQL which is the most widely used and well-known database query language which generates results in the form of rows and columns.

Database Query Types

  1. SELECT Query: It is used to retrieve data from a single table of a combination of multiple tables. SQL uses a SELECT statement to select, or extract, specific data based on the given base condition.
  2. ACTION Query: It is used to perform operations on the database such as insertion, deletion, modification, alteration, etc.

What is SubQuery?

A subquery is basically a SELECT statement that is embedded in a clause of another SQL statement. A subquery can be placed in:

  • SELECT clause.
  • FROM Clause.
  • WHERE Clause.
  • HAVING Clause.