T-SQL - DISTINCT Clause

The MS SQL Server DISTINCT keyword is used in conjunction with SELECT statement to eliminate all the duplicate records and fetching only unique records.

There may be a situation when you have multiple duplicate records in a table. While fetching such records, it makes more sense to fetch only unique records instead of fetching duplicate records.

Syntax

Following is the basic syntax of DISTINCT keyword to eliminate duplicate records.

SELECT DISTINCT column1, column2,.....columnN  
FROM table_name 
WHERE [condition] 

Example

Consider the CUSTOMERS table having the following records.

ID  NAME       AGE       ADDRESS            SALARY 
1   Ramesh     32        Ahmedabad          2000.00 
2   Khilan     25        Delhi              1500.00 
3   kaushik    23        Kota               2000.00 
4   Chaitali   25        Mumbai             6500.00 
5   Hardik     27        Bhopal             8500.00 
6   Komal      22        MP                 4500.00 
7   Muffy      24        Indore             10000.00 

Let us see how the following SELECT query returns duplicate salary records.

SELECT SALARY FROM CUSTOMERS 
   ORDER BY SALARY 

The above command will produce the following output where salary 2000 comes twice which is a duplicate record from the original table.

SALARY 
1500.00 
2000.00 
2000.00 
4500.00 
6500.00 
8500.00 
10000.00

Let us now use DISTINCT keyword with the above SELECT query and see the result.

SELECT DISTINCT SALARY FROM CUSTOMERS 
   ORDER BY SALARY 

The above command produces the following output where we do not have any duplicate entry.

SALARY 
1500.00 
2000.00 
4500.00 
6500.00 
8500.00 
10000.00