Histogram: Counting orders with variable bins in SQL - sql

Question

I have a table containing orders, items, and prices. I am trying to generate histograms for each item based on the prices.
Create Table #Customer_Pricing
(
customer_id int,
item_id VARCHAR(10),
qty DECIMAL(5,2),
price DECIMAL(5,2),
)
;
GO
-- Insert Statements
Insert into #Customer_Pricing values(128456, 'SOM 555', 8, 2.50)
Insert into #Customer_Pricing values(123856, 'SOM 554', 1, 2.50)
Insert into #Customer_Pricing values(123456, 'SOM 554', 55, 2.00)
Insert into #Customer_Pricing values(123556, 'SOM 555', 2, 2.20)
Insert into #Customer_Pricing values(123456, 'SOM 553', 12, 2.13)
;
For each item, I wanted 3 bins so I determined the bin sizes by dividing the difference of the MAX-MIN by 3, then adding that value to the MIN.
WITH Stats_Table_CTE (item_id2,max_p, min_p, int_p, r1_upper, r2_lower, r2_upper, r3_lower)
AS
( SELECT item_id
,max(price)
,min(price)
,(max(price) - min(price))/3
,min(price)+(max(price) - min(price))/3-0.01
,min(price)+(max(price) - min(price))/3
,min(price)+((max(price) - min(price))/3)*2-0.01
,min(price)+((max(price) - min(price))/3)*2
FROM #Customer_Pricing
GROUP BY item_id)
Now, I need to count the frequencies for each range and each item. I have attempted to do so by using SUM(CASE...) but was unsuccessful.
SELECT item_id
,SUM(CASE WHEN price <= r1_upper, THEN 1 ELSE 0 END) AS r1_count
,SUM(CASE WHEN price >= r2_lower AND <= r2_upper, THEN 1 ELSE 0 END) AS r2_count
,SUM(CASE WHEN price >= r3_lower, THEN 1 ELSE 0 END) AS r3_count
FROM Stats_Table_CTE
GROUP BY item_id
I also attempted to use COUNT in the form
SELECT item_id, price
count(price <= r1_upper) AS r1_count.... but I got stuck
In one attempt, INNER JOINed the #Customer_Pricing table and Stats_Table_CTE but didn't know where to go from there.
Ideally, I would like the output table to appear as follows: *This is not the actual data, but I included it to show the desired format of the output.
Item ID min_p r1_upper (r2 bins) r3_lower max_p r1_count r2_ct
SOM 553 2.00 2.16 saving space 2.33 2.50 2 1
SOM 554 2.13 2.48 2.88 3.25 1 0
SOM 555 2.31 2.51 2.72 2.92 3 2
*The format of the output table is off, but I have item ID, the bins, and the counts across the top grouped by item

Answer 1

Here is my recommendation:
WITH Stats_Table_CTE AS (
SELECT item_id, max(price) as maxprice, min(price) as minprice,
(max(price) - min(price))/3 as binsize
FROM #Customer_Pricing
GROUP BY item_id
)
SELECT cp.item_id,
SUM(CASE WHEN price < minprice + binsize THEN 1 ELSE 0
END) AS r1_count
SUM(CASE WHEN price >= minprice + binsize AND price < minprice+ 2*binsize
THEN 1 ELSE 0
END) AS r2_count
SUM(CASE WHEN price >= minprice + 2*binsize
THEN 1 ELSE 0
END) AS r3_count
FROM #Customer_Pricing cp JOIN
Stats_Table_CTE st
ON st.item_id = cp.item_id
GROUP BY cp.item_id
The important part is the join back to #Customer_Pricing. Also important is the simplification of the logic -- you can define the bounds for the bins and use <, rather than having a lower and upper bound for each one. Also, your query had some syntax errors in it.
Note that in many databases, the CTE would not be necessary because you could just use window functions. Your question is not tagged with the database (although I could guess what it is), so that change seems unwarranted.