Indicate variables from the Base Input SAS Data Set by which to merge. If left blank, these are assumed to be the same as the Corresponding Key Variables from Merge Input SAS Data Set.All of the variables in the base input data set are listed in the Available Variables field.
Scroll through the Available Variables field to find the desired key variables.
Left-click to highlight a single variable. Hold down the key while left-clicking to select multiple variables.
Once you have selected key variables, click the button to add them to the Key Variables from Base Input SAS Data Set field.