If you have worked with SQL, you will be familiar with the common types of SQL queries, such as SELECT, INSERT, UPDATE, and DELETE. But have you heard of DQL? DQL is a type of SQL query that is specifically designed for retrieving and manipulating data from a database. In this article gives you a good overview of DQL, what DQL in SQL means and its significance in data manipulation.
DQL Command in SQL
Hey guys, In a relational database management system, DQL full form is Data Query Language. Every RDBMS are using SQL to perform different operations where Data Query language plays a common part in SQL instructions.
Definition of DQL
Well, DQL full form is data query language that is a SQL component command similar to other programming languages that are used to query to fetch or retrieve data from the database. Basically, data query language commands are used to populate data from database objects like tables, views, etc. There is only one statement SELECT’ which shows attributes according to conditions applied in the WHERE clause. Query result data is compiled into a new temporary table before displaying when a select command is fired or executed.
Types of DQL Commands in SQL
There is only one type of DQL command in SQL database management systems – i.e. SELECT Command
Note: SELECT command is strictly a part of DQL (Data Query Language) in SQL but it is considered a part of DML. When the user adds either in FROM or WHERE clause and manipulates the data then it is considered a part of DML (Data Manipulation Language).
Key Elements of DQL in SQL
To understand how DQL works in SQL, it’s important to know the key elements of a DQL query-
- SELECT statement: This is the primary statement used in DQL. It specifies which columns to select from a table.
- FROM clause: This specifies the table from which to retrieve the data.
- WHERE clause: This is used to filter the data by a specific condition or set of conditions.
- ORDER BY clause: This is used to sort the data in ascending or descending order.
How Does DQL Work?
DQL works by querying a database and retrieving data that matches specific criteria. The SELECT statement is the most commonly used DQL command and is used to retrieve data from one or more tables. The FROM statement is used to specify which table or tables to query, while the WHERE statement is used to filter the data based on certain conditions.
Other DQL commands include the GROUP BY statement, which is used to group data based on specific criteria, and the ORDER BY statement, which is used to sort data in ascending or descending order. DQL also includes aggregate functions, such as COUNT, SUM, AVG, and MAX, which are used to perform calculations on data.
Overview Application of DQL Command
DQL has the functional capability of retrieval of data from databases which are organized by initial word statements. The SELECT statement comes under the Data Query Language as follows –
Syntax:
SELECT Expressions FROM Database_Object_Name WHERE Condition1 AND Condition2 AND ConditionN;
Applications of DQL in SQL
Refer below applications of Data query language in SQL –
1. Application
A simple select statement using * (All columns) from the desired table to retrieve the data as follows –
Syntax:
SELECT * FROM Table_Name;
Example:
USE SQLPOST GO SELECT * FROM Employee; GO
Screenshot: Below screenshot for reference –
In the above query result, all records from the Employee table with all columns data are displayed using an asterisk(*) sign.
Note: Asterisk (*) is used to fetch all the columns data of a table mentioned from clause
2. Application
A simple select statement taking all columns in place of asterisk (*) from the desired table to retrieve the data as follows –
Syntax:
SELECT Column1, Column2, ColumnN FROM Table_Name;
Example:
USE SQLPOST GO SELECT Employee_ID,Salutation,First_Name,Middle_Name,Last_Name,Full_Name,Department_ID,Gender,Date_Of_Birth,Mobile_No FROM Employee; GO
Screenshot: Below screenshot for reference –
In the above query result, all records from the Employee table with all columns data are displayed using column names in place of an asterisk(*) sign.
3. Application
A simple select statement taking a few columns from the desired table to retrieve the data as follows –
Syntax:
SELECT Column1, Column2, ColumnN FROM Table_Name;
Example:
USE SQLPOST GO SELECT Employee_ID,Salutation,First_Name FROM Employee; GO
Screenshot: Below screenshot for reference –
In the above query result, All records from the Employee table with specific columns data like Employee_ID, Salutation, and First_Name are displayed.
4. Application
The user can eliminate or exclude the duplicate records or data from a respective table using the DISTINCT command as follows –
Syntax:
SELECT DISTINCT Column1, Column2, ColumnN FROM Table_Name;
Example:
USE SQLPOST GO SELECT DISTINCT Employee_ID,Salutation,First_Name FROM Employee; GO
Screenshot: Below screenshot for reference –
In the above query result, All unique records from the Employee table with specific columns data like Employee_ID, Salutation, and First_Name are displayed. Users can put all columns’ names or asterisk (*) signs if all columns are needed.
5. Application
A simple select statement taking a few columns from the desired table to retrieve the data into ascending order as follows –
Syntax:
SELECT DISTINCT Column1, Column2, ColumnN FROM Table_Name; SELECT DISTINCT Column1, Column2, ColumnN FROM Table_Name ORDER BY Column1, Column2, ColumnN ASC;
Example:
USE SQLPOST GO SELECT DISTINCT Employee_ID,Salutation,First_Name FROM Employee; GO USE SQLPOST GO SELECT DISTINCT Employee_ID,Salutation,First_Name FROM Employee ORDER BY Employee_ID ASC; GO
Screenshot: Below screenshot for reference –
In the above query result, All unique records from the Employee table with specific columns data like Employee_ID, Salutation, and First_Name in ascending order are displayed. Users can put all columns’ names or asterisk (*) signs if all columns are needed.
6. Application
A simple select statement taking a few columns from the desired table to retrieve the data into descending order as follows –
Syntax:
SELECT DISTINCT Column1, Column2, ColumnN FROM Table_Name ORDER BY Column1, Column2, ColumnN DESC;
Example:
USE SQLPOST GO SELECT DISTINCT Employee_ID,Salutation,First_Name FROM Employee ORDER BY Employee_ID DESC; GO
Screenshot: Below screenshot for reference –
In the above query result, All unique records from the Employee table with specific columns data like Employee_ID, Salutation, and First_Name in descending order are displayed. Users can put all columns’ names or asterisk (*) signs if all columns are needed.
7. Application
A simple select statement taking a few columns from the desired table to retrieve the data using the WHERE clause as follows –
Syntax:
SELECT Column1, Column2, ColumnN FROM Table_Name WHERE Condition;
Example:
USE SQLPOST GO SELECT Employee_ID,Salutation,First_Name FROM Employee WHERE Employee_ID ='26'; GO
Screenshot: Below screenshot for reference –
In the above query result, Specific records from the Employee table with specific columns data like Employee_ID, Salutation, and First_Name displayed whose Employee_ID is 26.
8. Application
A simple select statement taking a few columns from the desired table to retrieve the data using the WHERE AND clause as follows –
Syntax:
SELECT Column1, Column2, ColumnN FROM Table_Name WHERE Condition1 AND ConditionN;
Example:
USE SQLPOST GO SELECT Employee_ID,Salutation,First_Name FROM Employee WHERE Employee_ID ='26' AND Salutation='Mr'; GO
Screenshot: Below screenshot for reference –
In the above query result, Specific records from the Employee table with specific columns data like Employee_ID, Salutation, and First_Name displayed whose Employee_ID is 26 and Salutation is Mr.
Advantages of DQL Command
- SELECT is used to fetch or retrieve data easily from database objects.
- SELECT in DQL is a standard command like bread and butter used in almost queries of DBMSs.
- To imagine SQL without data query language SELECT command is not possible
- SELECT is used to communicate with a database to query and get the data from a database object i.e. views and tables in second
- SELECT statement helps the user to analyze the query and data.
Best Practices for Using DQL in SQL
Here are some best practices to keep in mind when using DQL in SQL-
- Use specific column names instead of selecting all columns using the “*” wildcard.
- Use the WHERE clause to filter the data to only what you need, rather than retrieving all data and then filtering it manually.
- Use the ORDER BY clause to sort the data in a meaningful way.
FAQs
DQL commands are used to fetch data from database objects. There is only one statement – SELECT under data query language in SQL.
There is only one statement – SELECT in SQL.
No, DQL and DML aren’t the same because DQL is used to fetch the data from the database only but DML is used to manipulate the data from a database. The SELECT command is strictly a part of DQL (Data Query Language) in SQL but it is considered a part of DML. When the user adds either in FROM or WHERE clause and manipulates the data then it is considered a part of DML (Data Manipulation Language).
SELECT Column1, Column2, ColumnN FROM Table_Name;
Asterisk (*) is used to fetch all the column data of a table mentioned into from clause used in SQL.
Conclusion
DQL is an essential command tool for data analysis, reporting, and business intelligence. By learning the basics of DQL, you can begin to use the full potential of SQL and take your data analysis skills to the next level.
In this article, we discussed what is DQL in SQL, how it works, and its best practices in database management. We also provided some common DQL commands and answered some FAQs. With this knowledge, you can start using DQL in SQL and improve your database management skills.
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