Get current rank joining another table, MySql

Question

Sorry if I'm asking this, maybe it has a simple solution but I'm scratching my head for three days now and I can't find a good solution.

I have two tables, one defines "totals" and another table that defines "details".

Table_Totals

|item_id|user_rating| rating_count|
| 1     |      5.000|            5|
| 2     |      2.000|            3|
| 3     |      1.000|            5|
| 4     |      3.000|            2|
| 5     |      4.000|            8|

I can easily get the "rank" of each item_id by this query:

SELECT uo . * , (
     SELECT COUNT( * ) 
        FROM Table_Totals ui
        WHERE (ui.user_rating, ui.item_id) >= ( uo.user_rating, uo.item_id )
        ) AS rank
        FROM Table_Totals uo
    WHERE item_id = 3

So, I get this (global rank):

|item_id|user_rating| rating_count|rank|
| 3     |      1.000|            5|   5|

Now, I have also this table (that defines "details"):

Table_Details

|item_id|category| players|
| 1     |  arcade|     113|
| 2     |     RPG|      31|
| 3     |  arcade|     522|
| 4     |  arcade|     100|
| 5     |  MMORPG|      82|

My question is: how can I get the rank of a item_id BY category? How can I join these two tables and get something like this? (Keep in mind: item_id.Table_Totals = item_id.Table_Details).

I.E. rank for "arcade category":

|item_id|category| rank|
| 1     |  arcade|    1|
| 3     |  arcade|    3|
| 4     |  arcade|    2|

What's the best way to accomplish something similar?

Thank in advance to all!

Answer 1

Assuming a 1 to 1 relationship, and using user variables something like this (not tested):-

SELECT a.item_id, a.category, @rank:=@rank + 1 as rank
FROM Table_Details a
INNER JOIN Table_Totals b
ON a.item_id = b.item_id
CROSS JOIN (SELECT @rank:=0) Sub1
WHERE category = 'arcade'
ORDER BY b.user_rating DESC