Hi Stéphane, you can make any field a key field as long as each entry into the key field is unique.

If the second field is the key, you can have the following, even though the name field is the same:
name|ppp
name|rrr
name|ppr
name|prr
name|prp

If the second field is the key, you cannot have the following, even though the name is unique:
name1|ppp
name2|ppp
name3|ppp


Hope this helps with your planning.
Karen