Vim is not an IDE, and having a deep integration with things that are not directly related to text editing (like database management) within the editor is frowned upon.
That said, vi / Vim easily integrate with external tools, so if you have a handy command-line utility for managing Postgres, you can easily build your own mappings and commands to make frequently repeated tasks easier, mostly through :!
or :call system(...)
.
Quick and dirty Postgres query on the Vim Tips Wiki provides a starting point.