Question

I have a SQL Server 2008 DB with a table like this (Table1):

ID    ParentID    Name
--    --------    ---
11    NULL        Foo
12    11          Bar
13    12          etc 

ID is declared with IDENTITY.

I have the values Foo, Bar, etc as rows in another table (Table2) and I must insert them in Table1.

The inserted values must be in a parent child relation in Table1, with ParentID column from row N pointing to ID of row N-1.

Is it possible with one statement to insert the values with the relations between them?

Answer 1

-- Insert all names in first table
insert  Table1
        (Name)
select  Name
from    Table2

-- For each row in Table1,
-- Search for the matching row in Table2,
-- Then look up the "parent" row in Table2,
-- And back to Table1 for the "parent" id
update  t1
set     ParentID = t1_parent.ID
from    Table1 t1
join    Table2 t2
on      t1.Name = t2.name
cross apply
        (
        select  top 1 *
        from    Table2 t2_parent
        where   t2_parent.ID < t2.ID
        order by
                t2_parent.ID desc
        ) t2_parent
join    Table1 t1_parent
on      t1_parent.Name = t2_parent.Name