Need some SQL syntax help :-)
Both databases are on the same server
db1 = DHE
db2 = DHE_Import
UPDATE DHE.dbo.tblAccounts
INNER JOIN DHE_Import.dbo
Sorry its late, but I guess it would be of help to those who land here finding a solution to similar problem. The set clause should come right after the update clause. So rearranging your query with a bit change does the work.
UPDATE DHE.dbo.tblAccounts
SET DHE.dbo.tblAccounts.ControllingSalesRep
= DHE_Import.dbo.tblSalesRepsAccountsLink.SalesRepCode
from DHE.dbo.tblAccounts
INNER JOIN DHE_Import.dbo.tblSalesRepsAccountsLink
ON DHE.dbo.tblAccounts.AccountCode
= DHE_Import.tblSalesRepsAccountsLink.AccountCode