Not concatenation, more... err.. I don't know what you'd call it.
DISTINCT [C01241 Opened].[Col004] AS OpenerEmail,
[C01241 External Data].[DMCEMAIL] AS ExternalDataEmail,
[C01241 Internal Data].[Col15] AS InternalDataEmail
FROM [C01241 Opened]
LEFT JOIN [C01241 External Data] ON [C01241 External Data].[DMCEMAIL] = [C01241 Opened].[Col004]
LEFT JOIN [C01241 Internal Data] ON [C01241 Internal Data].[Col15] = [C01241 Opened].[Col004]
(Apologies for the table/col names, this is all very temporary)
So I've got a table, [C01241 Opened], which details all the people who registered. Those people might turn up in table [C01241 External Data], or they might turn up in [C01241 Internal Data]. Yes, they will always be in one or the other, and no, they won't appear in both.
At the moment, I just pull in the email address. But the client, of course, wants a whole bunch of fields that occur in the 'original data' tables: Firstname, Lastname, Company, Favourite color, etc.
What I want to know is if - and how - I can make the query output one column for each of the required fields, but populate it from either of the two 'original data' tables, depending on where their email address pops up in.