When you add the effective date field, the effective date criteria will automatically be added to your query to get the maximum effdt less than or equal to the current system date.
The following is a screenshot of the criteria for the effective date field. To view this, go the criteria tab, then edit the criteria on your effdt field. Based on your PeopleSoft version, this will probably look different, but the same concept still applies.
If you don't have this criteria, add the effdt field and add the criteria.
Note you can verify the correct criteria by looking at the SQL tab. You should see something that resembles this:
AND B.EFFDT =
(SELECT MAX(B_ED.EFFDT) FROM <RELEVANT_TABLE> B_ED
WHERE B.KEY1 = B_ED.KEY1
AND B_ED.EFFDT <= SUBSTRING(CONVERT(CHAR,GETDATE(),121), 1, 10))