Indicate variables from the Base Input SAS Data Set by which to merge data from the Merge Input SAS Data Set. The same variables must also exist in the Merge Input SAS Data Set.
Scroll through the Available Variables field to find the desired merge key variables.
Left-click to highlight a single variable. Hold down the key while left-clicking to select multiple variables.
Once you have selected the merge key variables, click the button to add them to the Merge Key Variables field.