MySQL - Get row number on select

Can I run a select statement and get the row number if the items are sorted?

I have a table like this:

mysql> describe orders;
+-------------+---------------------+------+-----+---------+----------------+
| Field       | Type                | Null | Key | Default | Extra          |
+-------------+---------------------+------+-----+---------+----------------+
| orderID     | bigint(20) unsigned | NO   | PRI | NULL    | auto_increment |
| itemID      | bigint(20) unsigned | NO   |     | NULL    |                |
+-------------+---------------------+------+-----+---------+----------------+

I can then run this query to get the number of orders by ID:

SELECT itemID, COUNT(*) as ordercount
FROM orders
GROUP BY itemID ORDER BY ordercount DESC;

This gives me a count of each itemID in the table like this:

+--------+------------+
| itemID | ordercount |
+--------+------------+
|    388 |          3 |
|    234 |          2 |
|   3432 |          1 |
|    693 |          1 |
|   3459 |          1 |
+--------+------------+

I want to get the row number as well, so I could tell that itemID=388 is the first row, 234 is second, etc (essentially the ranking of the orders, not just a raw count). I know I can do this in Java when I get the result set back, but I was wondering if there was a way to handle it purely in SQL.

Update

Setting the rank adds it to the result set, but not properly ordered:

mysql> SET @rank=0;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @rank:=@rank+1 AS rank, itemID, COUNT(*) as ordercount
    -> FROM orders
    -> GROUP BY itemID ORDER BY rank DESC;
+------+--------+------------+
| rank | itemID | ordercount |
+------+--------+------------+
|    5 |   3459 |          1 |
|    4 |    234 |          2 |
|    3 |    693 |          1 |
|    2 |   3432 |          1 |
|    1 |    388 |          3 |
+------+--------+------------+
5 rows in set (0.00 sec)

Take a look at http://www.fromdual.com/ranking-mysql-results">this</a>;.

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;

Swamibebop's solution works, but by taking advantage of table.* syntax, we can avoid repeating the column names of the inner select and get a simpler/shorter result:

SELECT @r := @r+1 , 
       z.* 
FROM(/* your original select statement goes in here */)z, 
(SELECT @r:=0)y;

So that will give you:

SELECT @r := @r+1 , 
       z.* 
FROM(
     SELECT itemID, 
     count(*) AS ordercount
	 FROM orders
	 GROUP BY itemID
	 ORDER BY ordercount DESC
    )z,
    (SELECT @r:=0)y;

You can use MySQL variables to do it. Something like this should work (though, it consists of two queries).

SELECT 0 INTO @x;

SELECT itemID, 
       COUNT(*) AS ordercount, 
       (@x:=@x+1) AS rownumber 
FROM orders 
GROUP BY itemID 
ORDER BY ordercount DESC; 

It's now builtin in MySQL 8.0 and MariaDB 10.2:

SELECT
  itemID, COUNT(*) as ordercount,
  ROW_NUMBER OVER (PARTITION BY itemID ORDER BY rank DESC) as rank
FROM orders
GROUP BY itemID ORDER BY rank DESC

SELECT RANK() OVER(ORDER BY Employee.ID) rank, forename, surname, Department.Name, Occupation.Name  
FROM Employee  
JOIN Occupation ON Occupation.ID = Employee.OccupationID  
JOIN Department ON Department.ID = Employee.DepartmentID 
WHERE DepartmentID = 2;