Probably someone here can explain it to me: It's clear that someone doing proprietary software on top of mysql have to get proprietary-compatible license for m

Probably someone here can explain it to me: It's clear that someone doing proprietary software on top of mysql have to get proprietary-compatible license for mysql. But. How this happens, that community submitted code/patches/etc gives Oracle profits? Isn't including any patch/code from GPL version into Proprietary version automatically enforce GPL rules and makes impossible to include this software into any other proprietary software? I saw this with other projects too. I am really interested how company behind product can provide both proprietary and gpl licenses for their products.