SQL - Distinct Keyword

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:

The basic syntax of DISTINCT keyword to eliminate duplicate records is as follows:

  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 |  +----+----------+-----+-----------+----------+

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 |  +----------+