data quality check against only one (real) database connector?

Is it possible to use only one db_connector to do exists test, or check uniqueness of a column. I noticed data-validation requires both -sc and -tc as parameters so that it always run a query on both of them.

Is it poosible to run query in one db connector and compare the result to a constant value (fake 2nd db connector but w/o actually doing connection and running query). This can be used to check existence of some counts to some known threshold value (like 0).

Basically this extends the feature to data quality check against one database but using a fake/dummy 2nd connector so that the API/CLI is still consistent?