我正在尝试在Linux Mint上安装postgresql：
sudo apt-get install postgresql
但是会收到以下错误消息：
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
postgresql : Depends: postgresql-12 but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
此问题可能是什么原因？