SQL - DISTINCT

The SQL 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:

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

Example:

Consider CUSTOMERS table is having 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 | +----+----------+-----+-----------+----------+

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

SQL> SELECT SALARY FROM CUSTOMERS ORDER BY SALARY;

This would produce 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:

SELECT DISTINCT SALARY FROM CUSTOMERS ORDER BY SALARY;

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

+----------+
| SALARY   |
+----------+
|  1500.00 |
|  2000.00 |
|  4500.00 |
|  6500.00 |
|  8500.00 |
| 10000.00 |
+----------+