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
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.