What does the DISTINCT keyword do in PROC SQL?

The DISTINCT keyword in PROC SQL is used to eliminate duplicate values from the result set. When a query is executed with the DISTINCT keyword, it ensures that each row in the result set is unique, preventing any repeated values based on the columns specified in the SELECT statement. This is particularly useful when you're only interested in unique combinations of values, such as when summarizing or filtering a dataset to only show distinct entries.

For instance, if you have a table containing multiple entries for the same customer and you want to retrieve a list of unique customers, using SELECT DISTINCT customer_name FROM customers; would yield a list where each customer appears only once, regardless of how many times they are recorded in the dataset.

This functionality contrasts with grouping datasets, sorting data, or limiting the number of columns, which are not the roles of the DISTINCT keyword. Each of those actions serves different purposes within SQL queries, such as organizing the output or focusing on specific attributes, but they do not directly address the elimination of duplicate entries.