SQL DISTINCT keyword

SQL DISTINCT keyword is used to retrieve unique ( distinct ) values from the table. If there are duplicate values present for a particular column, then SQL “distinct” keyword can be used to select only the distinct values.

SQL DISTINCT Syntax

SELECT DISTINCT column1, column2, columnN ..... FROM table_name;

where column1, column2, columnN are the column names of the table.

In this post, we are going to look at the below things one by one

• Using DISTINCT keyword on only one column
• Using DISTINCT keyword on multiple columns

Sample Table

Employee

Using DISTINCT on only one column

The following statement will display all of the DESIGNATION column values from the employee table.

SELECT DESIGNATION FROM Employee;

WITH DISTINCT

The following statement will display only the unique DESIGNATION from the employee table.

SELECT DISTINCT DESIGNATION FROM Employee;

Using DISTINCT on multiple columns

WITHOUT DISTINCT

select SALARY, DESIGNATION from employee;

WITH DISTINCT

Now, we will try to use the DISTINCT keyword on two of the columns ( SALARY and DESIGNATION ).

select DISTINCT SALARY, DESIGNATION from employee;

Here, we can see that the number of rows has been decreased by 1 after using the DISTINCT keyword. This is because the uniqueness will now be defined by the two columns combined ( Salary and Designation ) and that is the reason the row containing Principal Engineer designation and 60000.00 salary is printed only once, even though it was present two times in the actual table.

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