Number of unique name-feature pairs

[SDas]

I don't have ACCESS so I can't test this out, but this has a chance of working:

SELECT TAB2.FEATURE, SUM(IIF(ISNULL(TAB1.USERID),0,1) ) AS NumberUniqueUsers
FROM TAB2
       LEFT OUTER JOIN
       (SELECT DISTINCT USERID, FEATURE
        FROM TAB1
       ) AS TAB1B
         ON TAB2.FEATURE = TAB1B.FEATURE
GROUP BY TAB2.FEATURE

NOTE: This uses the same table data from my previous post.