So like this? Sorry I have not used SET Command before. I'm pretty new to SQL. This didnt work in this format, but I think it is wrong the way I set it up. It says:

Msg 156, Level 15, State 1, Line 7

Incorrect syntax near the keyword 'ON'.

Msg 156, Level 15, State 1, Line 65

Incorrect syntax near the keyword 'OFF'.

SET CONCAT_NULL_YIELDS_NULL {ON}

SELECT

(Select SUM (Amount) From Blah1.dbo.Paymenthistory)

+

(Select SUM (Amount) From Blah2.dbo.Paymenthistory)

As "Blah + Blah"

SET CONCAT_NULL_YIELDS_NULL {OFF}