SQL Server Challenging questions - look for 1st buyer, 2nd/3rd buyers, 4th or more buyers

Question

Happy Holidays, folks,

I am assigned to write a SQL query to show the number of buyers who purchase a particular product in a certain data range and in a location.
I need to find the following:

1. 1st time buyer ever.
2. 2nd/3rd time buyers.
3. 4th or more time buyers.

I was able to get the first time ever buyers using the queries below ; but unable to find the 2nd/3rd buyers, 4th or more buyers. Could someone please help.

DECLARE @from_dt        datetime
DECLARE @Day_End_dt     datetime

SET @from_dt =     '10/01/2010'
SET @Day_End_dt =  '12/29/2010'


select count(B.buyer_id) as California_1st_time_buyer
from
--LIST OF ALL BUYERS AND FIRST PURCHASED DATE THRU END OF DATE RANGE (10/1/98 - 12/28/10)
(select distinct buyer_id, min(purchased_date_time) as First_timer
from product_details
where purchased_date <@Day_End_dt
group by buyer_id
)A,
--LIST OF CALIFORNIA BUYERS AND FIRST PURCHASED DATE IN DATE RANGE (12/1/10 - 12/28/10)
(select distinct buyer_id, min(purchased_date_time) as First_timer_ca_in_date_range
from product_details
where purchased_date >=@from_d
and purchased_date <@Day_End_dt
and location = 'CA'
group by buyer_id
)B
where A.buyer_id = B.buyer_id
and A.First_timer = B.First_timer_ca_in_date_range



Input sample:
purchased_date_time     purchased_date      buyer_id
12/7/2010 12:30:00 PM       12/7/2010       5627242
--------------------------------------------------------------------
12/9/2010 4:30:00 PM         12/9/2010       9231374
12/19/2010 11:30:00 AM     12/19/2010      9231374
--------------------------------------------------------------------
12/9/2010 12:10:00 AM       12/9/2010       8061088
12/15/2010 5:00:00 PM       12/15/2010      8061088
12/21/2010 6:00:00 PM       12/21/2010      8061088
--------------------------------------------------------------------
12/1/2010 12:30:00 PM       12/1/2010       2288101
12/12/2010 6:30:00 PM       12/12/2010      2288101
12/27/2010 7:30:00 PM       12/27/2010      2288101
12/28/2010 6:30:00 PM       12/28/2010      2288101
--------------------------------------------------------------------
12/9/2010 10:45:00 AM       12/9/2010       2510454
12/16/2010 9:45:00 PM       12/16/2010      2510454
12/19/2010 4:19:00 AM       12/19/2010      2510454
12/22/2010 7:05:00 AM       12/22/2010      2510454
12/29/2010 2:30:00 AM       12/29/2010      2510454
--------------------------------------------------------------------
Output sample:
1st buyers =5 --count buyer_id who purchased the product first time ever in date range (12/1/10 - 12/28/10)

2nd/3rd buyers =7 --count buyer_id who purchased the product 2nd/3rd time in date range (12/1/10 - 12/28/10)

4th or more buyers =3  --count buyer_id who purchased the product 4th time or more in date range (12/1/10 - 12/28/10)

Please note these buyers are only from the date range mentioned above. Suppose if aa buyer had three purchases prior to 12/1/2010 and he purchased again on 12/1/2010, he would be considered as a 4th timer buyer.

Answer 1

I don't entirely understand what you want to do. If you could update the question with Table structure, a couple of sample rows and the expected output it would help.

Anyway, here is an attempt :)

The following query should give you a list of buyers that made four or less purchases. It isn't clear if you just wanted to count the purchases or if you need the actual purchase dates too, so I added the dates as well (for the first 4 purchases). If a buyer made only 1 purchase, the row would show NULL in purchase 2/3/4 columns.

If you want to include a range of dates or filter by location, those conditions would go in the inner select.

select buyer_id
      ,count(*) as purchases
      ,max(case when purchase_no = 1 then purchased_date end) as purchase_1
      ,max(case when purchase_no = 2 then purchased_date end) as purchase_2
      ,max(case when purchase_no = 3 then purchased_date end) as purchase_3
      ,max(case when purchase_no = 4 then purchased_date end) as purchase_4
  from (select buyer_id
              ,purchased_date
              ,row_number() over(partition by buyer_id
                                     order by purchased_date) as purchase_no
          from product_details
       )
 where purchase_no <= 4
group by buyer_id;

Let me know if it works.

Answer 2

This query will provide the buyer_id and number of purchases in the date range:

DECLARE @from_dt datetime
DECLARE @Day_End_dt datetime
SET @from_dt =     '10/01/2010'
SET @Day_End_dt =  '12/29/2010' 

SELECT [buyer_id],COUNT([buyer_id]) AS purchases_in_period
  FROM [product_details]
  WHERE purchased_date_time between @from_dt and @Day_end_dt
  -- OPTIONAL LOCATION FILTER
  -- AND [location] = 'CA'
  GROUP BY [buyer_id]
GO

If you use this as a nested query you can count the buyer_id values with a given number of purchases_in_period .

Answer 3

I would normally approach this as a union of separate queries.

      select buyer from T,  1 as FirstTimeBuyer, 0 as SecondTimeBuyer, 0 as thirdtimebuyer
      where date is in the specified range
      group by buyer having count(t.id) = 1
      UNION
       select buyer from T,  0 as FirstTimeBuyer, 1 as SecondTimeBuyer, 0 as thirdtimebuyer
      where date is in the specified range
      group by buyer having count(t.id) = 2
      UNION
       select buyer from T,  0 as FirstTimeBuyer, 0 as SecondTimeBuyer, 1 as thirdtimebuyer
      where date is in the specified range
      group by buyer having count(t.id) = 3