Get all customer having limited transactions - sql

Question

I have to extract all those customer names having transactions of less than 5000 each per month for 6 consecutive months and then have 3 transactions of 20,000 each on 7th month.
All the transactions for a customer will be stored in different rows.
Example: Considering customer A, Information for the customer will be stored as follows:
Name | TransactionDate | Amount
1. CustomerA | 27-08-2015 | 4500
2. CustomerA | 27-09-2015 | 4500
3. CustomerA | 27-10-2015 | 4500
4. CustomerA | 27-11-2015 | 4500
5. CustomerA | 27-12-2015 | 4500
6. CustomerA | 27-01-2016 | 4500
7. CustomerA | 27-02-2016 | 20000
8. CustomerA | 27-02-2016 | 20000
9. CustomerA | 27-02-2016 | 20000

Answer 1

Until you specify SQL flavor, I think I got a flexible and decent solution for T-SQL:
1) To have simpler queries, I have defined as persisted column to store month number is a convenient way:
create table CustomerTransaction
(
CustomerName VARCHAR(20),
TransactionDate DATE,
Amount NUMERIC(18, 2),
MonthNo AS DATEPART(yyyy, TransactionDate) * 12 + DATEPART(mm, TransactionDate) - 1 PERSISTED
)
If this cannot be used, you can employee date arithmetic (DATEDIFF), or have the exact computation inlined.
First CTE gets transaction data with a row number and a start month number for that group (customer and payment series).
For each category, small amounts and 20K (big amounts), I have selected from previous CTE applying filtering based on amount.
For each series apply the count criteria (6 small payments, followed by 3 big ones).
Join small and big payments based on customer and dates (group month is the smallest group month - 1).
The final query is the following:
declare #SmallAmountsLen INT = 6;
declare #BigAmountsLen INT = 3;
declare #SmallAmountThreshold NUMERIC(18, 2) = 5000
declare #BigAmount NUMERIC(18, 2) = 20000
;with AmountCte AS (
SELECT CustomerName, TransactionDate, Amount, MonthNo, ROW_NUMBER() OVER (PARTITION BY CustomerName ORDER BY TransactionDate) AS RowNo,
MonthNo - ROW_NUMBER() OVER (PARTITION BY CustomerName ORDER BY TransactionDate) AS GroupMonthNo
FROM CustomerTransaction
),
SmallAmountCte AS (
SELECT *
FROM AmountCte
WHERE Amount < #SmallAmountThreshold
),
BigAmountCte AS (
SELECT *
FROM AmountCte
WHERE Amount = #BigAmount
),
SmallGroupCte AS (
select CustomerName, GroupMonthNo
from SmallAmountCte
group by CustomerName, GroupMonthNo
having count(1) = #SmallAmountsLen
),
BigGroupCte AS (
select CustomerName, MonthNo
from BigAmountCte
group by CustomerName, MonthNo
having count(1) = #BigAmountsLen
)
select S.*, B.*
from SmallGroupCte S
join BigGroupCte B on B.CustomerName = S.CustomerName
where B.MonthNo = S.GroupMonthNo + #SmallAmountsLen + 1
[EDIT] Query without need of a computed column
declare #SmallAmountsLen INT = 6;
declare #BigAmountsLen INT = 3;
declare #SmallAmountThreshold NUMERIC(18, 2) = 5000
declare #BigAmount NUMERIC(18, 2) = 20000
;with AmountCte AS (
SELECT CustomerName, TransactionDate, Amount, DATEPART(yyyy, TransactionDate) * 12 + DATEPART(mm, TransactionDate) - 1 AS MonthNo,
ROW_NUMBER() OVER (PARTITION BY CustomerName ORDER BY TransactionDate) AS RowNo,
DATEPART(yyyy, TransactionDate) * 12 + DATEPART(mm, TransactionDate) - 1 - ROW_NUMBER() OVER (PARTITION BY CustomerName ORDER BY TransactionDate) AS GroupMonthNo
FROM CustomerTransaction
),
SmallAmountCte AS (
SELECT *
FROM AmountCte
WHERE Amount < #SmallAmountThreshold
),
BigAmountCte AS (
SELECT *
FROM AmountCte
WHERE Amount = #BigAmount
),
SmallGroupCte AS (
select CustomerName, GroupMonthNo
from SmallAmountCte
group by CustomerName, GroupMonthNo
having count(1) = #SmallAmountsLen
),
BigGroupCte AS (
select CustomerName, MonthNo
from BigAmountCte
group by CustomerName, MonthNo
having count(1) = #BigAmountsLen
)
select S.*, B.*
from SmallGroupCte S
join BigGroupCte B on B.CustomerName = S.CustomerName
where B.MonthNo = S.GroupMonthNo + #SmallAmountsLen + 1

Answer 2

Here is a simpler query to get the result, what I wanted:
WITH CTE
AS
(
SELECT * FROM
(
SELECT DENSE_RANK() OVER (PARTITION BY Name ORDER BY DATEPART(MONTH,TransactionDate)) AS SrNo,
Name,Amount,DatePart(Month,TransactionDate) AS MonthNo,TransactionDate FROM TransactionTable) AS A
WHERE
(Amount <= 5000 AND SrNo < 7) OR (Amount = 20000 AND SrNo = 7)
)
SELECT A.Name AS Account_Number,A.Transaction_Date FROM
(
SELECT Name,Amount,COUNT(SrNo) As Sr,MAX(TransactionDate) AS Transaction_Date FROM CTE
WHERE SrNo = 7 AND Amount = 20000
GROUP BY Name,Amount
HAVING COUNT(srNo) = 3) AS A
INNER JOIN
(
SELECT Name,COUNT(SrNo) AS Ss FROM CTE
WHERE SrNo < 7 AND Amount <= 5000
GROUP BY Name
HAVING COUNT(srNo) = 6) AS B
ON A.Name = B.Name