PostgreSQL, OpenSSL, and the GPL

Anything that's "purely functional" -- e.g., it's the only possible way to accomplish something, like talk to a MySQL server -- is by definition not covered by copyright. What that means in particular cases is not always obvious...

There's a plausible argument that the existence of libedit means that psql *per se* is not a derived work of readline. But that doesn't matter for people who are shipping psql+readline compiled together -- that combination is *clearly* a derived work of both.