Query between two versions of the Database at runtime

One of my clients was using two versions of the same database and wanted a simple way to be able to check a condition in a query and switch between the two versions at runtime. Here’s a simple way to do it

Note: For demonstration purposes, I am pretending to check a condition in the form of the variable @Chk

DECLARE @Chk As Bit = 1

SET @Chk = 1

IF  @Chk = 1
    USE New_DB 
ELSE 
    USE Old_DB 
     
SELECT custid,custname FROM Customers

Now if @Chk = 1, then the query will be executed against the New_DB. Similarly if @Chk is not 1, the Old_DB will be selected.