Finding top 5 worst performing customers by salesperson - sql

Question

I have a view that returns data as follows:
| salesman | customer | invoiced | budgeted | difference
|--------------|--------------|-------------|-------------|--------------
| Joe | ACME Ltd | 1000 | 2000 | -1 000
| Sam | Apple | 1500 | 1100 | +400
| Joe | Apple | 2000 | 2300 | -300
| Kim | ACME Ltd | 1000 | 1500 | -500
This is a snippet of of over 1500 rows that are returned. What I would like to do is return all rows by salesman showing that salespersons 5 worst customers sales. Each salesperson would therefore have 5 rows and each salesperson does sell to various customers who can be the same customer as another salesperson... right now I am looking at 5 worst customers by salesperson by value.
Any ideas on how I can achieve this?

Answer 1

Since one salesman can invoice the same company multiple times, you need to average the invoice amount across that group, then rank withing that partition and take the top five. If you are looking for the absolute worse sale per salesman then you would need to replace AVG with MIN.
SELECT
*
FROM
(
SELECT
salesman,
customer,
AverageInvoiced,
DescendingRank=DENSE_RANK() OVER(PARTITION BY salesman ORDER BY AverageInvoiced DESC)
FROM
(
SELECT
salesman,
customer,
AverageInvoiced=AVG(invoiced)
FROM
Table
WHERE
GROUP BY
salesman,
customer
)
)AS A
WHERE
DescendingRank<=5

Answer 2

I think you can use this
TRy This
SELECT
*
FROM
(
SELECT
salesman,
customer,
AverageDiffrence,
DescendingRank=DENSE_RANK() OVER(PARTITION BY salesman ORDER BY AverageDiffrence DESC)
FROM
(
SELECT
salesman,
customer,
AverageDiffrence=AVG(difference)
FROM
ireports_salesman_variance
WHERE
GROUP BY
salesman,
customer
)
)AS A
WHERE
DescendingRank<=5