resolve the issue

How would you check the uniqueness of a data set? i.e. that the data set was unique on its primary key (ID). suppose there were two Identifier variables: ID1, ID2

Thank you Sir

proc FREQ order = FREQ;
tables ID;
shows multiples at top of listing
Or, compare number of obs of original data set and data after
proc SORT nodups
or is that
proc SORT nodupkey
use first.ID in data step to write non-unique to separate data set if first.ID and last.ID then output UNIQUE; else output DUPS;