Query to select distinct name based on several factors
Assuming the data is constrained to avoid duplicates, how about something like this?  This is assuming Microsoft SQL Server syntax.

SELECT United.PolicyName FROM
(SELECT PolicyName FROM dbo.Policies 
WHERE Setting = 'DiskUsage'
  AND State = 'Enabled'
  AND Value = 1
UNION ALL
SELECT PolicyName FROM dbo.Policies 
WHERE Setting = 'Memory'
  AND State = 'Enabled'
  AND Value = 1
) AS United
GROUP BY United.PolicyName
HAVING COUNT(*) = 2


RESULTS: Default

This specifically queries for each of the states that you care about.  Since there are two requirements, then the UNION will produce two rows when both selects are find a row.