The APPEND Procedure
Another way to combine SAS data sets is to append one data set to another using the APPEND procedure. Although appending and concatenating are similar, there are some important differences between the two methods. Whereas the DATA step creates an entirely new data set when concatenating, PROC APPEND simply adds the observations of one data set to the end of a “master” (or BASE) data set. SAS does not create a new data set nor does it read the base data set when executing the APPEND procedure.
To append SAS data sets, you specify a BASE= data set, which is the data set to which observations are added and then specify a DATA= data set, which is the data set containing the observations that are added ...