Få antal procent av en post i en enda fråga

COUNT(*) OVER() ger dig det totala antalet.

Redigera Men egentligen behöver du SUM(COUNT(MyTbl.ItemID)) OVER() eftersom du summerar värdena i den kolumnen.

SELECT Items.ItemID,
       [count] = COUNT(MyTbl.ItemID),
       [Percent] = 100.0 * COUNT(MyTbl.ItemID) / SUM(COUNT(MyTbl.ItemID)) OVER()
FROM   (VALUES (1,'N1'),
               (2,'N2'),
               (3,'N4'),
               (4,'N5')) Items(ItemID, ItemName)
       LEFT JOIN (VALUES(1),
                        (1),
                        (3),
                        (4),
                        (4),
                        (4)) MyTbl(ItemID)
         ON ( MyTbl.ItemID = Items.ItemID )
GROUP  BY Items.ItemID
ORDER  BY Items.ItemID