Question

I have a database table with parent child relationships between different rows.
1 parent can have any number of children.
Children do not have children.
I want to copy ‘Message’ from ‘Parent Category’ to child categories.

CategoryID   Name           Value       Message      ParentID     DeptId
1            Books          9           Specials                  1
2            Music          7                                     1
3            Paperback      25                       1            1
4            PDFs           26                       1            2
5            CDs            35                       2            1

If that was sample data, Paperback should have Specials as it’s Message after the query is run.
I have gotten the child rows (the query runs very slow, don’t know why), but how do I get the data and assign it to appropriate child rows?

--@DeptId = 1
select * from Categories
where ParentID in(
select CategoryID from Categories 
where DeptID = @DeptId
)

I would like to see a solution that would not use cursors.

Thanks

Answer 1

A JOIN across two copies of the table as child & parent should do the job (and I’m fairly sure this is valid in SQL Server). It looks for non-NULL ParentID on the child table and copies Message from the associated ParentID row.

UPDATE c
  SET c.Message = p.Message
FROM
  Categories c
  INNER JOIN Categories p ON c.ParentID = p.CategoryID
WHERE 
  c.ParentID IS NOT NULL
  AND c.DeptID = @DeptID