This qualifier (and its synonym DISTINCTROW) allows you to weed out multiple entries when they contain the same data. For instance, suppose that you want a list of all authors in the table. If you select just the author column from a table containing multiple books by the same author, you’ll normally see a long list with the same author names over and over. But by adding the DISTINCT keyword, you can show each author just once. So let’s test that out by adding another row that repeats one of our existing authors.
SELECT DISTINCT author FROM classics;