What Is A Query (Database Query)?


Query is a request to an information system to get information for the specific information in which parameters are defined inside the query. The query is mainly used as a database term where database servers are queried for different types of information.

Query Parameters

An information or database system generally provides a lot of different types, sizes, and structures of information. In order to get the information we want we need to specify some parameters during the query. The Query Parameters can be specified in different ways for different query languages. But as generally similar parameter names and logic is used.

  • Return names starting with letter A
  • Return all information about the people whose age is over 65
  • Return class name of all students from all people data

Query Metrics and Performance

Another important part of a query is its performance. Query Performance is related to the remote information or database system performance with the query type, returned information and the network connection. Especially enterprise-level applications require reliable and high performance to work smoothly so different query optimization techniques are used.

Query Languages

Querying a remote information or database system is related to the remote information or database system installed software. In general database systems are categorized as Relational and Non-Relational. This categorization sets the query language, as well as the platform of the client, also provides different query language which are translated into the remote database system and software language.

SQL (Strcutured Query Language) is the most popular query language. SQL is used by the Relational Database Management Systems (RDMS) in order to provide requested information in a generic, fast and standardized way. SQL is supported by all major RDMS. SQL is also used as a base for a lot of popular query programming languages like PSQL, PL/SQL, T-SQL, etc.

Select Name, Surname, Age From People Where Age > 65

LINQ (Language Integrated Query) is as its name suggests a programming language integrated query language that is provided by the .NET framework and its programming languages C#, F#, VB.NET. The query is created by using programming language structures like from , where ,select new , foreach etc which are similar to the SQL language keywords.

var results =  from c in SomeCollection
               where c.SomeProperty < 10
               select new {c.SomeProperty, c.OtherProperty};

foreach (var result in results)
{
        Console.WriteLine(result);
}

CQL (Cassandra Query Language) is the query language used for the NoSQL database system named Cassandra. CQL is influenced by RDMS where a lot of SQL structures are used inside the CQL. The following example will query for the user’s name and occupation that userid is one of 199, 200, 207.

SELECT name, occupation FROM users WHERE userid IN (199, 200, 207);

XQuery (XML Query) and XPath are other popular query languages that are mainly used to query XML based or structured data. XQuery and XPath are mainly used to parse and query structured markup languages like XML, HTML, XHTML, etc.

Google Search Engine Language is a different type of query language that is used by millions of people every day. Google Search Engine provides some basic query language structures in order to make a Google search in a precisely defined way. Following query search the term “poftut.com” in all over the web except the domain “poftut.com” by using -site: parameter.

"poftut.com" -site:poftut.com

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