To arrange the hierarchy in a table - sql

Question

I have a table dbo.Hierarchy that contains the following data:
Level1 Level2 Level3 Level4 Level5 Level6 Level7 Level8 Level9 Level10
-----------------------------------------------------------------------
a b c d e f g h i j
k l m n o
There are a total of 10 levels and any item can have hierarchy upto any level. In the above data a is the parent of b, b is the parent of c and so on. j and o are the last levels in their respective hierarchies. How can I get the output in the below format:
Name ParentName LevelID
-------------------------------
a NULL 1
b a 2
j i 10
k NULL 1
l k 2
o n 5

Answer 1

Something like (untested)
with t(L1,L2,L3,L4,L5,L6,L7,L8,L9,L10) as (
values ('a','b','c','d','e','f','g','h','i','j')
, ('k','l','m','n','o',null,null,null,null,null)
)
select x.*
from t
cross apply (
values (L1,null,1),(L2,L1,2),(L3,L2,3),(L4,L3,4),(L5,L4,5)
, (L6,L5,6),(L7,L6,7),(L8,L7,8),(L9,L8,9),(L10,L9,10)) x (name, parentname, levelid)
where name is not null

Answer 2

Try this:
;with base as
(select *, row_number() over (order by level1) rn from tbl),
src as
(
select
valname as name,
cast(substring(colname,6,len(colname)) as int) as level,
rn from
(select * from base) s
unpivot
(
valname
for colname in ([level1],[level2],[level3],[level4],[level5],[level6],[level7], [level8],[level9],[level10])
) u
),
cte as
(select * from src
where level = 1
union all
select s.* from src s
inner join cte c on s.level = c.level + 1 and s.rn = c.rn)
select distinct s.name, t.name parentname, s.level levelid from
cte s
left join cte t on s.rn = t.rn and s.level = t.level + 1
Breakdown:
CTE base is used to generate row number as a derived column. We will use this column to keep track of which values belong to which row. This will help in uniquely mapping children to their parents.
CTE src is where we transform the table from this denormalised structure to a normalised one. Using UNPIVOT, we reduce the data set to 3 columns - name, level and the row number rn.
CTE cte is a recursive CTE that we use to get all possible combinations of parents and children (including immediate parents as well as ancestors).
Finally, we LEFT JOIN cte to itself on the condition that row number is same on both sides of the join i.e. the values belong to same record from the base table, and also that the value from the right side is the immediate ancestor (parent) of the value on the left side.
Demo
The huge mass of code above can be avoided, if you were to choose a normalised structure for your table. I would suggest something like this:
CREATE TABLE tbl
(ID int, --Keep track of values that are related to each other
Name varchar(100), --Name
Level int --The level for a particular value
)
With this proposed structure, all you would need is the recursive CTE (cte from the above code) and the left join to get the parent-child data. The beauty of this approach is that you can extend it to any number of levels that you like, without having to hard-code the level numbers.
Demo