How to query the V shaped data? - sql

Question

TxnID RunningAmount MemberID
==================================
1 80000 20
2 90000 20
3 70000 20 //<==== Falls but previously never below 100k, hence ignore
4 90000 20
5 110000 20
6 60000 20 //<==== Falls below 100k, hence we want ID 8
7 80000 20
8 120000 20
9 85000 28
...
....
How to construct the query such that it group by members, get the first transactionID that formed the "V" shape. Even a pseudocode is fine, I can't share my attempt because I am totally clueless about how to do it.
UPDATES:
Sorry for the lack of explanations on the conditions. The base amount we looking is 100k. ID is random, definitely we need to have rownumber
We ignore all transactions before ID = 5 because their runningAmount is never exceeded 100k.
Now when ID=5, exceeded 100k, we check if transactions after ID=5 if there is a down trend in runningAmount that falls below 100k.
Immediately we see ID=6 falls below 100k, so we want to find the first transaction that exceed 100k again(if there is).
From the data sample above, the expected result is only one record, which is ID=8.
For every member, there will only be either one or zero record found based on the conditions I've mentioned

Answer 1

Try this query:
declare #tbl table(TxnID int, RunningAmount int, MemberID int);
insert into #tbl values
(1, 80000, 20),
(2, 90000, 20),
(3, 70000, 20),
(4, 90000, 20),
(5, 110000, 20),
(6, 60000, 20),
(7, 120000, 20),
(8, 85000, 28);
select TxnID, RunningAmount, MemberID,
LAG(VShape) over (partition by MemberID order by TxnID) VShape
from (
select TxnID, RunningAmount, MemberID,
case when rn < lagrn and rn < leadrn then 1 else 0 end VShape
from (
select *,
LAG(rn) over (partition by MemberID order by TxnID) lagRn,
LEAD(rn) over (partition by MemberID order by TxnID) leadRn
from (
select TxnID,
RunningAmount,
MemberID,
ROW_NUMBER() over (partition by MemberID order by RunningAmount) rn
from #tbl
) a
) a
) a
Last column VShape indicates if value in RunningAmount completes V shape (although you could be more clearer on what it means instead of everybody figuring it out). Now you can filter values based on RunningAmount (wheter they fall below or above 100k).
Here is version for earlier versions of SQL Server that don't have LAG and LEAD functions:
;with cte as (
select *,
ROW_NUMBER() over (partition by MemberID order by RunningAmount) rn
from #tbl
), cte2 as (
select c1.TxnID, c1.RunningAmount, c1.MemberID, c1.rn, c2.rn [lagRn] , c3.rn [leadRn]
from cte c1
left join cte c2 on c1.TxnID = c2.TxnID + 1 and c1.MemberID = c2.MemberID
left join cte c3 on c1.TxnID = c3.TxnID - 1 and c1.MemberID = c3.MemberID
), cte3 as (
select TxnID, RunningAmount, MemberID,
case when rn < lagrn and rn < leadrn then 1 else 0 end VShape
from cte2
), FinalResult as (
select c1.TxnID, c1.RunningAmount, c1.MemberID, c2.VShape
from cte3 c1
left join cte3 c2 on c1.TxnID = c2.TxnID + 1 and c1.MemberID = c2.MemberID
)
select fr.*, fr2.RunningAmount RunningAmountLagBy2 from FinalResult fr
left join FinalResult fr2 on fr.TxnID = fr2.TxnID + 2
where fr.RunningAmount > 100000 and fr2.RunningAmount > 100000 and fr.VShape = 1
UPDATE
After question update, here's solution:
select TxnID from (
select *, ROW_NUMBER() over (partition by VShape order by TxnID) CompletesVShape from (
select TxnID,
RunningAmount,
MemberID,
sum(case when RunningAmount >= 100000 then 1 else 0 end) over (partition by MemberID order by TxnID rows between unbounded preceding and current row) VShape
from #tbl
) a
) a where VShape > 1 and CompletesVShape = 1

Answer 2

Based on your question update and assuming for V shape necessary condition is to get above and below running amounts > 100000 and middle be smaller than above and below running amounts, below is a query showing how to do it in 2008 sql server.
also see live demo
; with firstlargeamount as
(
select MemberId, minTrxid=min(TxnID)
from t
where RunningAmount>100000
group by MemberId
)
,tbl as
(
select *,
rn=row_number() over( partition by MemberId order by TxnId)
from
t
)
select t3.*,f.*
from tbl t1
join tbl t2
on
t1.memberId=t2.memberid and t1.rn=t2.rn +1
and t1.RunningAmount<t2.RunningAmount
join tbl t3
on
t1.memberId=t3.memberid and t1.rn=t3.rn -1
and t1.RunningAmount<t3.RunningAmount
join firstlargeamount f
on
f.Memberid=t2.memberid and f.minTrxid>=t1.TxnID
Explanation:
First step is to generate a row number sequence at member level as cte tbl and min limiting transaction in cte firstlargeamount
Second step is double self join to find above and below records per row which satisfy the V shape criteria as well join with firstlargeamount to find rows which satisfy the 100000 criteria
Note that the above and below records are simply found using +1/-1 from the current records's row number computed in the step 1