Some time ago, I required a specific version of PostgreSQL. After searching on all the repositories, I was unable to find that specific version. It seems that the PostgreSQL community removes the old package when a new minor version comes. For example, if you need the 12.2 version but the 12.3 version is out, its [&]

https://www.percona.com/blog/2021/01/28/how-to-create-postgresql-custom-builds-and-debian-packages/