Adding unique keys

It is sometimes possible to identify a table by keys other than the primary
ones. These are (combinations of) columns that have
key characteristics (unique and non null); they are called unique keys.
Unique keys are preceded by a sequential number enclosed in brackets: <1> for the
first unique key, <2> for the second, etc.
To create an alternate key:
- Look for the Key tool
and click the arrow next to the key (a display
of keys numbered 1 to 5 will appear).
- Choose one of those numbered keys.
- Click the column(s) that will become the unique key.