Question

I am using SQL Server 2008. I have a table like this:

UnitId ParentId  UnitName
---------------------------
1        0       FirstUnit
2        1       SecondUnit One  
3        1       SecondUnit Two
4        3           B
5        2           C
6        4           D
7        6           E
8        5           F

I want to get second parent of the record. For example:

If I choose unit id that equal to 8, It will bring unit id is equal to 2 to me. It needs to be SecondUnit One. or If I choose unit id that equal to 7, It will bring unit id is equal to 3 to me. It needs to be SecondUnit Two.

How can I write a SQL query this way?

Answer 1

It took me a while, but here it is 🙂

with tmp as (
  select unitId, parentId, unitName, 0 as iteration
  from t
  where unitId = 7
  union all
  select parent.unitId, parent.parentId, parent.unitName, child.iteration + 1
  from tmp child
  join t parent on child.parentId = parent.unitId
  where parent.parentId != 0
)
select top 1 unitId, parentId, unitName from tmp
order by iteration desc

Here is also a fiddle to play with.