Videos
One trap, under a minute
Each one shows a single failure that does not announce itself — no warning in the log, no error, just a wrong number downstream.
0:43 The many-to-many merge that silently multiplies rows
A SAS MERGE with duplicate BY values does not warn. It just returns more rows than you started with.
0:48 NODUPKEY deletes data and tells you nothing
PROC SORT NODUPKEY drops records without a note in the log. What you lose depends on sort order.
0:45 PROC FREQ hides your missing values by default
Percentages are computed on non-missing rows unless you ask otherwise. Your denominator is wrong.