MySQL - Get row number on select
Take a look at this.
Change your query to:
SET @rank=0;
SELECT @rank:=@rank+1 AS rank, itemID, COUNT(*) as ordercount
FROM orders
GROUP BY itemID
ORDER BY ordercount DESC;
SELECT @rank;
The last select is your count.
SELECT @rn:=@rn+1 AS rank, itemID, ordercount
FROM (
SELECT itemID, COUNT(*) AS ordercount
FROM orders
GROUP BY itemID
ORDER BY ordercount DESC
) t1, (SELECT @rn:=0) t2;