How to Use DISTINCT in SQL

Problem:

You’d like to query your data to return the result without duplicate rows. Imagine you have a table with repeated entries, and you only want each unique entry to show up once. This helps in getting a cleaner and more concise set of results, making analysis easier.

Example:

Our database has a table named books with data in the columns author_firstname, author_lastname, and book_title. You’d like to get a list of unique first and last names of the authors.

Solution:

We’ll use the SQL DISTINCT clause to remove duplicate rows. Here’s the query:

SELECT DISTINCT
   author_firstname,
   author_lastname
FROM books;

Here’s the result of the query:

Discussion:

The DISTINCT clause is used in the SELECT statement to filter out duplicate rows in the result set. You can use DISTINCT when you select a single column, or when you select multiple columns as we did in our example. This is especially useful when you want to simplify your dataset and focus on unique records, making data analysis more efficient and accurate.