About GPL and proprietary software

I don't feel very confident when it comes to software licenses. But
there are some cases I would like to make myself clear. What I am
particulary interested in is when does GPL license become restrictive?
For example say a company has a proprietary software product that only
works with MySQL and no other database system. Are the following cases
legal?
1) This company sells his product under proprietary license and leaves
it up to the client to set up required MySQL server. Or perhaps helps
the client with seting up MySQL with or without extra fee.
2) Clients pay monthly fee to this company for using their proprietary
software which uses MySQL hosted in the companys server.
3) This company sells his product under proprietary license on the CD
which also includes MySQL as free bonus (with source code).

If these cases are valid, then when does GPL license for MySQL (or any
other software in that matter) become truly restrictive for a
proprietary company?

Kaarel