QGIS DBManager Query between Shapefile and PostgreSQL Table

I have an instance of DB Manager running and I have TWO connections present in the left pane of the DB manager form.

1. First connection is to a static shapefile on my local file system
2. Second connection is to a PostgreSQL DB-table

I would like to run a compound query between the two in DB Manager.

However, The problem is when you instantiate an SQL window it is either associated with one or another connection. Any suggestions.

Is there a way to perform such a query with in QGIS Manager.

I am running QGIS v2.18.11 and we do not have any shp plugins, availabl e and nor the means to download them