Date: Wed, 3 Dec 2014 07:42:16 -0700 (MST)
From: Ron256 <ejaluronaldlee@gmail.com>
To: pgsql-sql@postgresql.org
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Subject: Re: generating the average 6 months spend excluding first orders
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I have modified my query but I am really wondering why I am getting incorrect
results.
Please see the following link. http://sqlfiddle.com/#!15/5897e/4.

I am getting the same values for both Average 1 year spend and Average 6
months spend which might not be right. 

Explaining further, the CTE in the demo generates the first time orders of a
customer which I exclude in the join when calculating the the Average Six
months spend per year. 


WITH first_cust_cte AS (
         SELECT o_1.persistent_key_str,
            min(o_1.ord_submitted_date) AS ord_date
           FROM orders o_1
          GROUP BY o_1.persistent_key_str
        ), 
first_time_customer_orders_to_be_excluded_cte as
(
 SELECT o.persistent_key_str,
    o.ord_id
   FROM orders o
     JOIN first_cust_cte c 
    ON o.persistent_key_str = c.persistent_key_str
    AND o.ord_submitted_date = c.ord_date
) 

-- 1 row per year
SELECT EXTRACT(YEAR FROM ord_submitted_date) AS ordered
    
       , AVG(o.item_extended_actual_price_amt)::numeric(18,2)
"Avg_6_months_spend"
FROM  (SELECT generate_series(min(ord_submitted_date)  -- single query ...
                            , max(ord_submitted_date)  -- ... to get min /
max
                            , '1d')::date FROM orders) g
(ord_submitted_date) 
LEFT   join orders o USING (ord_submitted_date)
LEFT   JOIN first_time_customer_orders_to_be_excluded_cte c
USING(persistent_key_str)
WHERE  o.ord_submitted_date >= g.ord_submitted_date -  interval '6 MONTHS'
AND    ord_submitted_date   <=  g.ord_submitted_date + interval '6 MONTHS'
AND c.ord_id <> o.ord_id
GROUP BY 1
ORDER BY 1


Can someone help me out? I know someone out there has a solution.


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