I suggested reinstalling gdm3 to hopefully get gdm3 to work properly.
But if you removed sql and it removed gnome-control-center, then it is a safe bet that it took the desktop, too.
To be safe... I think you should definitely reinstall the Zorin desktop.
sudo apt install --reinstall zorin-os-desktop
Or
sudo apt install zorin-os-desktop
Doing this will also install gdm3, zorin-appearance and a lot of other stuff, including anything that the removal of sql took with it.