SQL Select UNION add database name

I am creating several UNION queries to eventually combine data from 3 different company databases.

One of the current queries looks like this:

SELECT     DocEntry, DocNum, DocType, CANCELED, DocStatus, DocDate, CardCode, CardName, NumAtCard, DocTotal, GrosProfit, Ref1, VatSumSy, DiscSumSy, TaxDate,
                      ShipToCode, OwnerCode, SlpCode
FROM         OINV
UNION ALL
SELECT     DocEntry, DocNum, DocType, CANCELED, DocStatus, DocDate, CardCode, CardName, NumAtCard, DocTotal, GrosProfit, Ref1, VatSumSy, DiscSumSy, TaxDate,
                      ShipToCode, OwnerCode, SlpCode
                     
FROM ORIN      

I want to add the database name or the company name to all queries so I can later combine them or pull the data from each company  separately.

If I can't get the database name, a column with a text field for each would be fine.
I just need to add it to every query. ie: "ABC" "XYZ" or "MMM"

How can I do this?