In PROC SQL, what is the effect of using the DISTINCT keyword?

Using the DISTINCT keyword in PROC SQL is specifically designed to remove duplicate rows from the output of a query. When applied, it ensures that each row in the result set is unique, meaning that if there are multiple rows in the data that are identical across all selected columns, only one instance of such rows will be present in the final output.

For example, if a dataset contains several identical entries like (1, 'John'), (1, 'John'), and (2, 'Jane'), using DISTINCT in a SELECT statement will yield one (1, 'John') and one (2, 'Jane'), effectively condensing the data to unique rows only.

This functionality makes it a powerful tool in data analysis and reporting, where redundancy often skews results and insights. Ultimately, using DISTINCT provides clarity and accuracy in datasets where duplicate records could mislead interpretations. The other options do not accurately represent what DISTINCT does within PROC SQL, as it does not modify the underlying data structure, add new rows, or count unique values directly.