DQL Full Form

Data Query Language (DQL) is a component of Structured Query Language (SQL) focused on retrieving data from databases using the SELECT statement.

It allows users to extract specific information based on defined criteria, enabling efficient data analysis and decision-making. In this article, We will learn about the DQL Full Form in detail by understanding various aspects in detail.

Introduction to Data Query Language (DQL)

• Structured Query Language (SQL) is a nonprocedural language used for retrieving data from queries. It was introduced by IBM as a part of the R project. It was declared as a standard language by ANSI and ISO. DQL statements are used for performing queries on the data within schema objects.
  
• The purpose of the DQL Command is to get some schema relation based on the query passed to it. 
  
• We can define DQL as follows it is a component of SQL statement that allows getting data from the database and imposing order upon it.
  
• It includes the SELECT statement. This command allows getting the data out of the database to perform operations with it.
  
• When a SELECT is fired against a table or tables the result is compiled into a further temporary table, which is displayed or perhaps received by the program i.e. a front-end. Data Query Language (DQL) or Data Retrieval Language (DRL).

Data Query Language has commands that retrieve the data from the query. It has a single command: select.  It has subcategories: 

• DDL or Data Definition Language has commands like create, rename, and alter. 
• DML or Data Manipulation Language has commands like update, insert, and delete. 
• DCL or Data Control Language has commands like grant and revoke. 
• TCL or Transaction Control Language has commands like rollback, and commit.  

Characteristics of Data Query Language (DQL)

It is used for retrieving data. A user can retrieve data according to his/her requirements using the select command. 

1. Data Retrieval: DQL is used only to retrieve data.
2. Flexibility in query: The SELECT statement enables a user to obtain specific data based on criteria or conditions.
3. Data Ordering: It keeps the results sorted and filtered. This way, work on database data becomes even more structured and organized.
   
   Example: 
   If a user wants to retrieve all the from the employee table, the query must be given as follows: 

select *
from employee;  

asterisk mark (*) indicates that all the rows are retrieved from the table. 

If a user wants to know the average salary of the employees, the query must be given as follows: 

select avg(salary) 
from employee; 

This displays the average salary of the employees. 
Here asterisk mark isn't needed as we need to retrieve only particular rows. 

If a user wants to know the name of the employee whose salary is less than 10, 000; the query is: 

select ename 
from employee 
where salary<=10, 000; 

A condition is placed to retrieve the data and a relational operator is used as well. 

Advantages of DQL

• SELECT is a standard command used for almost every query.
  
• It can also be written as SELECT as SQL is a case-insensitive language.
  
• It makes the data retrieving process easier.
  
• No coding is needed.
  
• This domain language can be used for communicating with the databases and receive answers to complex questions in seconds.

Disadvantages of DQL

• Data Query Language has no disadvantages.
  
• It is not possible to imagine Structured Query Language without the select command.
  
• Interfacing a DQL database is more complex than adding a few lines of code.
  
• The operating cost of some DQL versions makes it difficult for some programmers to access them.

Applications of DQL

• Analytical Queries.
  
• Retrieve Information from the database.
  
• Modify the index structures and database table.
  
• Such questions are analytical in nature and DQL is used abundantly to run analytical queries in retrieving worthwhile knowledge from data.
  
• Database Information Retrieval: This helps in retrieving a certain information from the database for achieving a task, such as employee's details or sales records, etc.
  
• Modify Index Structures: DQL creates modifications in database structures. To enable improved queries, indexing is also done.

Conclusion

Lastly, Data Query Language (DQL) is a component of DBMS that can really retrieve data from relational databases using the power that is simple. It allows the user to select query-efficiently with the combination and the application of a basic command: SELECT. Other benefits, such as the simple interfacing and low operating costs of some systems, do offset its limitations.