[DMDB] Fix a few issues, more intuition on normal forms

semester4/dmdb/parts/01_sql/03_query-language/03_aggregation.tex

@@ -5,7 +5,7 @@
 whose output should be evident.
 
 Please note that you cannot use the aggregation functions and still output another column,
-as they produce a single value.
+as they produce a single value. (Except you are grouping on that value)
 
 For each of the functions, you can optionally specify \texttt{DISTINCT}.