Sql maximum record per group question

Question

CREATE
TABLE DBO.TEST
ID INT
, RECTYPE
INT,SEQ
INT, MAX0
INT,MAX1
INT,MAX2
INT)
INSERT
INTO dbo.TEST
SELECT
1,1,1,3,2,3
UNION
ALL
SELECT
1,2,2,3,2,3
UNION
ALL
SELECT
1,2,3,3,2,3
UNION
ALL
SELECT
1,1,2,3,2,3
--SELECT * FROM dbo.TEST
how
to find
MAX seq
for each ID
and Rectype
My result should be
MAX0
is maximum
of seq
group
by ID
MAX1
is maximum
of seq
group
by ID
where rectype
=1
MAX2 id maximum
of seq
group
by ID
where rectype
= 2
ID Rectype   SEQ  MAX0     MAX1      MAX2
1 1      1     3      2        3
1 2      2     3      2        3
1 2      3     3      2        3
1 1      2     3      2        3

Answer 1

This is a typical in-group computation, which can be performed through the following steps:
1. Group the data by ID; each group has all data of an ID.
2. Perform in-group computation: compute the maximum value of SEQ in this group and assign the result to MAX0.
3. In-group computation: select in this group the records whose Rectype equals 1, compute the maximum value of SEQ and assign it to MAX1.
4. In-group computation: select in this group the records whose Rectype equals 2, compute the maximum value of SEQ and assign it to MAX2. 
The train of thought is clear, but it is difficult to write code for in-group computations in SQL. You have to transform the computation to the form that multi-layer relations are nested into N window functions.
But the code will be complicated and difficult. I’m afraid you still won’t be able to figure it out the next time you run into the similar problem. I suggest you using esProc to help with the computation if there is not so much data. Because esProc supports
in-group computation very well, you can solve the problem in it easily. The code in esProc is as follows: 
IDs=test.group(ID)   //corresponds to step 1
       IDs.run(~.run(MAX0=IDs.~.max(SEQ)))          //step 2
       IDs.run(~.run(MAX1= IDs.~.select(Rectype==1).max(SEQ)))     //step 3
       IDs. run(~.run(MAX2= IDs.~.select(Rectype==2).max(SEQ)))    //step 4
In the code, “~” represents each group. It is similar to a loop variable. And, steps 2, 3 and 4 can be integrated into one step:
       =IDs.run(~.run(MAX0=IDs.~.max(SEQ)), ~.run(MAX1= IDs.~.select(Rectype==1).max(SEQ)), ~.run(MAX2= IDs.~.select(Rectype==2).max(SEQ)) )          
The computed result in the above is in the form of ResultSet, which is easy to integrate with Java or the reporting tool.