Which statement is used to read data from an existing SAS dataset?

The SET statement is used to read data from an existing SAS dataset. When you want to process or manipulate data that is already stored in a SAS dataset, the SET statement allows you to access that dataset directly within a DATA step. By using the SET statement, you can perform operations such as data transformation, subset selection, and variable creation or modification, all while retaining access to the original dataset.

For example, if you have a dataset named "sales_data" and you want to create a new dataset that includes modified or additional variables based on the existing data, you would use the SET statement to read "sales_data" into your DATA step. This allows you to reference and work with the data easily.

Other statements, such as the DATA statement, are vital for creating new datasets or defining programming blocks, while the PROC statement typically invokes a procedure that performs analysis or reporting on data. The INPUT statement is used specifically for reading raw data into a SAS dataset during the data step, not for accessing existing datasets. Thus, the SET statement is the most appropriate choice for reading from an existing SAS dataset.