SQL SELECT DISTINCT Statement

The SQL SELECT DISTINCT Statement is used to retrieve unique records (by removing the duplicates) from the specified Column in the SELECT Statement. In this article, we will show you, How to write SQL DISTINCT with an example.

SQL SELECT DISTINCT syntax

The basic syntax of the SELECT DISTINCT in SQL Server can be written as:

-- SQL Server SELECT DISTINCT Statement
SELECT DISTINCT [Column Names]
FROM Source
WHERE Conditions -- This is Optional

• DISTINCT: Returns Unique Columns
• Columns: It allows us to choose the number of columns from the tables. It may be One or more.
• Source: One or more tables present in the Database. JOINS are used to join multiple tables.

We are going to use the below-shown data to explain the Select Distinct in SQL Server with an example.

SQL Distinct on Single Column

In this example, We are going to select the unique records present in the Education Column using SQL server Distinct.

-- SQL Select Distinct on Single Column Example
USE [SQLTEST]
GO
SELECT DISTINCT [Education]
  FROM [Employees]

OUTPUT

SQL Distinct Multiple Columns

When we use the SQL Select Distinct on the multiple columns, the SELECT Statement returns the unique combination of multiple columns instead of unique individual records.

In this example, We are going to select the unique combination records present in the Education Column and Yearly Income Column.

-- SQL Select Distinct Multiple Columns Example
SELECT DISTINCT [Education]
	,[YearlyIncome]
  FROM [Employees]

OUTPUT

Although we used the DISTINCT Keyword in the SELECT Statement, from the above screenshot you can observe that it is returning duplicates because

• Bachelors and 70000 is a Unique Combination
• Bachelors and 80000 is a Unique Combination
• and Bachelors and 90000 is a Unique Combination

SQL DISTINCT WHERE Clause

In this example, we will show you, How to use the DISTINCT in SQL Select Statement along with WHERE Clause. The following statement will return the Distinct Education values whose Yearly Income is greater than 50000

-- SQL Select Distinct Where Example
SELECT DISTINCT [Education]
	,[YearlyIncome]
  FROM [Employees]
  WHERE YearlyIncome > 50000

OUTPUT

NOTE: The SQL DISTINCT consider the NULL records as a valid unique record so, Please use any Not Null function (NOT NULL) functions to remove NULLS.

SQL Distinct Group By Example

The SQL Server Distinct also allows you to use Aggregate Functions along with Group By Clause.

The following Query groups the employees by Education. Next, it finds the Sum of Distinct Yearly Income for each Education group.

-- SQL Select Distinct Group By Example
SELECT [Education]
	,SUM(DISTINCT  YearlyIncome) AS [Total Income]
  FROM [Employees]
  GROUP BY [Education]

OUTPUT

Let me remove the Distinct Keyword from the above query.

-- SQL Select Distinct Group By Example
SELECT [Education]
	,SUM(YearlyIncome) AS [Total Income]
  FROM [Employees]
  GROUP BY [Education]

OUTPUT

From the below screenshot you can see the difference in yearly Income. Because it is finding the sum of all the records (not the Distinct ones).

SQL Distinct Count Example 1

This SQL Select Distinct Count is one of the most commonly asked questions. This example counts and returns the distinct employee Ids in each Education group.

-- SQL Select Distinct Count Example
SELECT [Education]
	,COUNT(DISTINCT EmpID) AS [Total Employees]
  FROM [Employees]
  GROUP BY [Education]

OUTPUT

SQL Distinct Count Example 2

Here, we used Count Function with the Distinct keyword, and without Distinct. This will show the difference between the result set.

-- SQL Select Distinct Count Example
SELECT [Education]
	,COUNT(DISTINCT DeptID) AS [Total Dept Ids]
	,COUNT(DeptID) AS [Total Ids]
  FROM [Employees]
  GROUP BY [Education]

OUTPUT

SQL Distinct Null Example

The SQL Select Distinct statement considers NULL as a distinct one. You can see the same in below example.

-- SQL Select Distinct Example
SELECT DISTINCT DeptID
  FROM [Employees]

OUTPUT

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