Original post mashed the code frag...
Frank Hamersley (12/8/2008)
... if it isn't why not simply fix the dynamic sql to look like (after creating the CustomerMaster table) ....
IF Exists(SELECT Customer FROM CustomerMaster WHERE Customer = @Customer)
SELECT data FROM CustomerMaster WHERE Customer = @Customer
ELSE
[Build the usual dynamic SQL]
Then fix the Customer insert(s) to use CustomerMaster and instigate a background process to "migrate" rows from the old to new table.
I take your point about avoiding if possible a big bang changeover - but it may not be avoidable. If not you will just have to re-engineer from the ground up. To take my previous posts building analogy you may have to almost tear down the entire building and start again.
Cheers, Frank.