Select ID from #Temp where Left(id,6) IN (Select left(id,6) from #Temp group by left(id,6) having count(*) > 1)

SELECT ID                              --I'm assuming the column name is ID, substitute the true column name
FROM TableName t1                      --I'm giving your table this generic table name, substitute the true table name
WHERE EXISTS (
  SELECT *
  FROM TableName t2                    --substitute the true table name here as well
  WHERE LEFT(t2.ID,6) = LEFT(t1.ID,6)  --substitute the true column name here as well  
  AND t2.ID <> t1.ID
  )
ORDER BY ID

DECLARE @T TABLE (ProductID VARCHAR(50))

INSERT INTO @T
SELECT '003223' UNION ALL SELECT '003225' UNION ALL SELECT '003227'
UNION ALL SELECT '003227A' UNION ALL SELECT '003236' UNION ALL SELECT '003236A'
UNION ALL SELECT '003241' UNION ALL SELECT '003273' UNION ALL SELECT '003273A'

SELECT ProductID
FROM (
    SELECT ProductID, m=MAX(n) OVER (PARTITION BY LEFT(ProductID, 6))
    FROM (
        SELECT ProductID
            ,n=ROW_NUMBER() OVER (PARTITION BY LEFT(ProductID, 6) ORDER BY (SELECT NULL))
        FROM @T) a) b
WHERE m > 1