In order to avoid that side effect, a simple solution might be this,
create a temporary table, and use data via that table.
Here is a very simple example:
CREATE TABLE #tmp_date(datetime mydate,int idagent); INSERT INTO #tmp_date (mydate, idagent) SELECT GETDATE() as MyDate, ID FROM Agents; UPDATE Campaigns SET Campaigns.FieldDate = A1.MyDate FROM Campaigns AS C1 JOIN #tmp_date AS A1 ON C.IDAgent = A1.ID; DROP TABLE #tmp_date;