Question

I have a table structure with columns like this

• [ID]
• [Name]
• [ParentId]
• [ParentName]

The parents are contained in the same table, and i would like to populate the parent name column using a statement like:

UPDATE Table
   SET ParentName = (select Name  
                      from Table 
                     where Id = ParentId)

When i do this, all the ParentNames are set to null. Thoughts?

Answer 1

Here’s another T-SQL syntax you can use :

(BTW, I agree with cletus about the denormalization concerns.)

-- create dummy table
create table test (id int, name varchar(20), 
parentid int, parentname varchar(20))

go

-- add some rows 
insert test values (1, 'parent A', null, null)
insert test values (2, 'parent B', null, null)
insert test values (3, 'parent C', null, null)

insert test values (11, 'child A 1', 1, null)
insert test values (12, 'child A 2', 1, null)
insert test values (33, 'child C 1', 3, null)

go

-- perform update
update c set parentname = p.name from test c join test p on c.parentid = p.id 

go

-- check result
select * from test