Top 10 for multiple Categories

Here is a generalized version of what I used to see the top 5 customers for each sales team based on revenue, in case it's a good starting point for someone else. The query assumes that the data has already been grouped, so In my case, I first wrote a transform to group the data based on the Sales Team and Customer, summing the Revenue for each record.  These fields have been generalized as Group_Field, Item_Field, and Measure_Field, respectively, in the code below.

SELECT
    `Group_Field` -- The column that indicates the group of records for which we want to find the top n records
    , `Item_Field` -- The thing of which we want to find the top n for each group
    , `Measure_Field` -- The column we used to order the records so we know which are the top n
FROM
    (
        SELECT
            `Group_Field`
            , `Item_Field`
            , `Measure_Field`
            /* Gives an incremental row number if the group hasn't changed. If it has, it starts over at 1. */
            , (@row_num := CASE WHEN @Group_Variable = `Group_Field` THEN @row_num + 1 ELSE 1 END) as row_number
            /* Updates the value of @Group_Variable so it can be used in the next iteration */
            , (@Group_Variable := Group_Field) as `notUsed`
        FROM
            data_grouped_by_group_field_and_item_field -- Replace with name of table containing grouped values
            , (SELECT @row_num := 0) n -- Initializes @row_num variable to 0
            , (SELECT @Group_Variable := '') t -- Initializes @Group_Variable  to empty string
        ORDER BY
            `Group_Field`
            , `Measure_Field`
    ) sub_select
WHERE
    /* Use this to indicate how many Item records to return for each Group (currently set to 5) */
    sub_select.row_number <= 5


-- END OF QUERY

This query adds row numbers to records within each group in the subquery, allowing you to restrict the number of records coming back by setting the max row number you care about in the WHERE clause.