The final SQL statement should have read:

SELECT V.value_type,
CASE V.value_type
WHEN 'COUNT' THEN COUNT(*)
WHEN 'SUM' THEN SUM(S.my_value)
WHEN 'MAX' THEN MAX(S.my_value)
WHEN 'MIN' THEN MIN(S.my_value)
END
FROM Source S
INNER JOIN Value_Types V ON 1=1
GROUP BY V.value_type

I left out the GROUP BY clause in my original post.

-Tom.