I have released a library that allows you to use MySQL, Postgres and Sqlite3 together. the library name is db_wrapper.
There is an official database library for Nim, but it does not implement connection pooling. However, this library (db_wrapper) allows connection pooling to be set at connection time. This library (db_wrapper) implicitly sets the same value as the connection pool as idle connection when connecting. There is a 9 second difference in performance between db_mysql and db_mysql for 150,000 queries issued.
Check it :)