identifies a variable
that appears in the BY statement in the PROC PRINT step. If the value
of the BY variable changes, or if the value of any BY variable that
precedes it in the BY statement changes, PROC PRINT prints the sums
of all variables listed in the SUM statement.
Details
What Variables Are Summed?
If you use a SUM statement,
PROC PRINT subtotals only the SUM variables. Otherwise, PROC PRINT
subtotals all the numeric variables in the data set except for the
variables listed in the ID and BY statements.