TSQL query to concatenate and remove a common prefix

Question

I have some data

id    ref
==   ==========
1    3536757616
1    3536757617
1    3536757618

and want to get the result

1    3536757616/7/8

so essentially the data is aggregated by id with the combined refs links separated by a slash '/', but with the removal of any common prefix, so if the data looked like

id    ref
==   ==========
2    3536757628
2    3536757629
2    3536757630

I would like to get the result

2    3536757629/28/30

I know that I can just concatenate links using

SELECT distinct
    id,
    stuff ( ( SELECT
                  '/ ' + ref 
              FROM
                  tableA tableA_1
              where tableA_1.id = tableA_2.id
    FOR XML PATH ( '' ) ) , 1 , 2 , '' )
from TableA tableA_2

To give

1   3536757616/ 3536757617/ 3536757618
2   3536757628/ 3536757629/ 3536757630

but this is a bit that removes the common element that I am after .....

---

Code for test data:

create table tableA (id int, ref varchar(50))

insert into tableA
select 1, 3536757616
union select 1, 3536757617
union select 1, 3536757618
union select 2, 3536757628
union select 2, 3536757629
union select 2, 3536757630

Answer 1

WITH hier(cnt) AS
        (
        SELECT  1
        UNION ALL
        SELECT  cnt + 1
        FROM    hier
        WHERE   cnt <= 100
        )
SELECT  CASE WHEN ROW_NUMBER() OVER (ORDER BY id) = 1 THEN ref ELSE ' / ' + SUBSTRING(ref, mc + 1, LEN(ref)) END 
FROM    (
        SELECT  MIN(common) AS mc
        FROM    (
                SELECT  (
                        SELECT  MAX(cnt)
                        FROM    hier
                        WHERE   SUBSTRING(initref, 1, cnt) = SUBSTRING(ref, 1, cnt)
                                AND cnt <= LEN(ref)
                        ) AS common
                FROM    (
                        SELECT  TOP 1 ref AS initref
                        FROM    tableA
                        ) i,
                        tableA
                ) q
        ) q2, tableA
FOR XML PATH('')

---

3536757616 / 17 / 18 / 28 / 29 / 30

Same thing with groups:

WITH hier(cnt) AS
        (
        SELECT  1
        UNION ALL
        SELECT  cnt + 1
        FROM    hier
        WHERE   cnt <= 100
        )
SELECT  (
        SELECT  CASE WHEN ROW_NUMBER() OVER (ORDER BY a2.ref) = 1 THEN ref ELSE ' / ' + SUBSTRING(ref, mc + 1, LEN(ref)) END 
        FROM    tableA a2
        WHERE   a2.id = q2.id
        FOR XML PATH('')
        )
FROM    (
        SELECT  id, MIN(common) AS mc
        FROM    (
                SELECT  a.id,
                        (
                        SELECT  MAX(cnt)
                        FROM    hier
                        WHERE   SUBSTRING(i.initref, 1, cnt) = SUBSTRING(a.ref, 1, cnt)
                                AND cnt <= LEN(ref)
                        ) AS common
                FROM    (
                        SELECT  id, MIN(ref) AS initref
                        FROM    tableA
                        GROUP BY
                                id
                        ) i
                JOIN    tableA a
                ON      i.id = a.id
                ) q
        GROUP BY
                id
        ) q2
---
3536757616 / 7 / 8
3536757628 / 29 / 30

Answer 2

I named my table #T and used the following SELECT statement

select id, number, substring(#t.ref, 1, v.number), count(id)
from master.dbo.spt_values v
inner join #t on v.number <= len(#t.ref)
where v.name is null and v.number > 0 
group by id, number, substring(#t.ref, 1, v.number)
order by id, count(id) desc, number desc

, .

, : , SELECT TOP 1 .

Answer 3

declare @tableA table(id int, ref varchar(50))
declare @suffix table(id int, suffix varchar(50))
declare @todo table(id int)

insert into @tableA
select 1, '3536757616'
union select 1, '3536757617'
union select 1, '3536757618'
union select 2, '3536757628'
union select 2, '3536757629'
union select 2, '3536757630'

insert into @suffix
select * from @tableA

insert into @todo
select s1.id
from (
    select id, cnt = count(*)
    from @suffix
    group by id, substring(suffix, 1, 1) 
  ) s1 
  inner join (
    select id, cnt = count(*)
    from @suffix
    group by id
  ) s2 on s2.id = s1.id and s2.cnt = s1.cnt

while exists (select * from @todo)
begin
  update @suffix
  set suffix = substring(suffix, 2, len(suffix) - 1)
  from @suffix s
       inner join @todo t on t.id = s.id

  delete from @todo

  insert into @todo
  select s1.id
  from (
      select id, cnt = count(*)
      from @suffix
      group by id, substring(suffix, 1, 1) 
    ) s1 
    inner join (
      select id, cnt = count(*)
      from @suffix
      group by id
    ) s2 on s2.id = s1.id and s2.cnt = s1.cnt  
end

select * from @suffix