SQL - Handling Duplicates with DISTINCT keyword

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.

SQL>select * from CUSTOMERS;

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 

First, let us see how the following SELECT query returns duplicate salary records:

SQL> SELECT SALARY FROM CUSTOMERS
     ORDER BY SALARY;

This would produce the following result where salary 2000 is coming 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 

Now, let us use DISTINCT keyword with the above SELECT query and see the result:

SQL> SELECT DISTINCT SALARY FROM CUSTOMERS
     ORDER BY SALARY;

This would produce the following result where we do not have any duplicate entry:

SALARY 
  1500.00 
  2000.00 
  4500.00 
  6500.00 
  8500.00 
 10000.00