MariaDB Distinct

Summary: in this tutorial, you will learn how to use the MariaDB distinct to select distinct rows from a table.

Introduction to the MariaDB distinct option

A select statement may return some identical rows. To explicitly specify that you want to remove duplicate rows from the result set, you use the distinct option:

select 
    distinct column_name
from 
    table_name;
Code language: SQL (Structured Query Language) (sql)

In this syntax, the distinct keyword appears after the select keyword and before columns or expressions of the select list.

The query will return only distinct values from the column_name in the table_name.

The distinct option can also be applied to multiple columns as shown in the following statement:

select
    distinct column1, column2,...
from
    table_name;
Code language: SQL (Structured Query Language) (sql)

In this case, the query will use the combinations of values in all the columns, which appear after the distinct option, to evaluate the distinction of rows.

Note that if you want to select distinct values of some columns only, you use the group by clause.

MariaDB distinct examples

We’ll use the country_stats table from the nation sample database for demonstration:

A) Using the MariaDB distinct with one column

The values in the year column repeats for each country.

select 
    year
from 
    country_stats
order by 
    year;
Code language: SQL (Structured Query Language) (sql)

The following statement uses the distinct option to select the distinct years from the the year column:

select 
    distinct year 
from 
    country_stats
order by   
    year desc;
Code language: SQL (Structured Query Language) (sql)

MariaDB distinct with null

In MariaDB, the distinct option treats null values the same. In other words, if you use the select distinct to query data from a column that has null values, the distinct option will keep only one null value.

See the countries table from the sample database:

The following statement uses the distinct option to select unique national days:

select 
    distinct national_day
from 
    countries;
Code language: SQL (Structured Query Language) (sql)

Even though, many rows have null values in the national_day column, the distinct option keeps only one value.

In this tutorial, you will learn how to use the MariaDB distinct to select distinct rows from a table.