SQL SELECT DISTINCT statement

The SELECT DISTINCT statement is used to retrieve only unique or distinct records from a database table. This query retrieves all the distinct values of a column in a table.

Syntax

The basic syntax of the SELECT DISTINCT statement is as follows:

SELECT DISTINCT column1, column2
FROM table_name;

Here, column1 and column2 are the names of the columns that we want to retrieve unique values from. table_name is the name of the table from which we want to retrieve the data.

Example

Consider a table named employee with columns id, name, department, and salary. The following SQL query will retrieve all the distinct values of the department column from the employee table:

SELECT DISTINCT department
FROM employee;

Output

The output of the above query will be a list of all the unique departments in the employee table.

department
----------
Sales
Marketing
Finance
Human Resources

Explanation

The SELECT DISTINCT statement works by eliminating all the duplicate values from the result set and only returning the distinct values. In the example above, we want to retrieve all the unique or distinct departments from the employee table.

Use

The SELECT DISTINCT statement is mostly used to retrieve unique values from a table. It can also be used with aggregate functions like COUNT(), MAX(), etc. to get the unique results.

Important Points

• The DISTINCT keyword is used to retrieve only the unique values from the result set.
• SELECT DISTINCT statement works with a single or multiple columns.
• It eliminates the duplicate values from the result set.

Summary

In summary, the SELECT DISTINCT statement is used to retrieve unique or distinct values from a table. It is handy when we want to eliminate duplicate values from the result set. It can also be used with aggregate functions to fetch unique or distinct results.