Question

I often find when I am pulling data for analysis, that I group the number of orders a customer has placed into ranges, such as:

1-2
3-5
6-9
10-12
13-15

I do this with a CASE function. However, when you get the query results, the order ranges will be listed like:

1-2
10-12
13-15
3-5
6-9

This easy to correct in Excel when you have 1 query and a few order range groups. However, when you’re pulling many queries, it’s a pain to correct this over and over.

What is the best way to pull a range and have it ordered correctly?

here’s an example of the query I would write:

SELECT 
    OrderRange = CASE
        WHEN COUNT(OrderID) BETWEEN 1 AND 5 THEN '1-5'
        WHEN COUNT(OrderID) BETWEEN 6 AND 10 THEN '6-10'
        WHEN COUNT(OrderID) > 10 THEN '10+'
        ELSE 'Error'
    END
FROM Orders
GROUP BY CASE
    WHEN COUNT(OrderID) BETWEEN 1 AND 5 THEN '1-5'
    WHEN COUNT(OrderID) BETWEEN 6 AND 10 THEN '6-10'
    WHEN COUNT(OrderID) > 10 THEN '10+'
    ELSE 'Error'
    END
ORDER BY...  ?

Answer 1

I’d keep a table of ranges, e.g. (indices not written)

CREATE TABLE Ranges (RangeSet int, MinVal int, MaxVal int, Name varchar(50));

and then e.g.

INSERT INTO ranges VALUES
  (1,1,5,'1-5'),(1,6,10,'6-10'),(1,11,-1,'11+'),
  (2,1,10,'1-10'),(2,11,20,'11-20'),(2,21,30,'21-30'),(2,31,-1,'31+');

you get the idea. Now you do something like (table and field names free fiction)

SELECT
  CustomerID,
  count(OrderID) AS OrderCount
FROM Orders
WHERE <whatever, e.g order_date BETWEEN ... AND ...>
GROUP BY CustomerID
HAVING OrderCount>0

as you’d normally would expect, but wrap it in a superquery joining to the Ranges table

SELECT
  BaseView.CustomerID as CustomerID,
  Ranges.Name as OrderRange
FROM (
  SELECT
    CustomerID,
    count(OrderID) AS OrderCount
  FROM Orders
  WHERE <whatever, e.g order_date BETWEEN ... AND ...>
  GROUP BY CustomerID
  HAVING OrderCount>0
) AS BaseView
INNER JOIN Ranges ON
  Ranges.RangeSet=<id-of-required-rangeset>
  AND BaseView.OrderCount>=Ranges.MinVal
  AND (BaseView.OrderCount<=Ranges.MaxVal OR Ranges.MaxVal=-1)
ORDER BY RangeSet.MinVal DESC
;

Now you just have to supply the RangeSet you want to apply, maybe creating a new one on occasion.

Disclaimer: This is a performance-killer