Computed Column with relationships - sql-server-2008

Question

I have a table, MapLocation, which has a column and two relationships with tables that have a field that really need to be displayed as a single concatenated value. I was thinking this was a perfect case for a computed column, but not sure how to go about it.
MapLocation MaoNo Section
_____________________ _____________________ _____________________
MapNoId MapNoId SectionId
SectionId MapNumber (int) Section (int)
Identifier (nvarchar)
LocationName (nvarchar)
LocationName = "MapNUmber - SectionNumber - Identifier"
ex: 20 - 03 - SW4
How would I write that? I haven't done much with computed columns or concatenating in SQL.
Edit:
I need an actual computed column that is automatically updated, im looking for the formula. Or is this more of a function/trigger? Its possible, I certainly barely know what I'm doing. The idea is that I dont want to have to do two more server calls and concatenate these values client side.

Answer 1

You would use something like this to get the value:
select cast(n.MapNumber as nvarchar(10)) + ' - ' -- cast the MapNumber
+ cast(s.SectionId as nvarchar(10)) + ' - ' -- cast the SectionId
+ l.Identifier
from MapLocation l
left join MaoNo n
on l.MapNoId = n.MapNoId
left join Section s
on l.SectionId = s.SectionId
Then if you need to perform an UPDATE:
update l
set l.LocationName = (cast(n.MapNumber as nvarchar(10)) + ' - '
+ cast(s.SectionId as nvarchar(10)) + ' - '
+ l.Identifier)
from MapLocation l
left join MaoNo n
on l.MapNoId = n.MapNoId
left join Section s
on l.SectionId = s.SectionId
Edit #1 - you can use a TRIGGER:
CREATE TRIGGER trig_LocationName
ON MapLocation
AFTER INSERT
AS
Begin
update MapLocation
set LocationName = (cast(n.MapNumber as nvarchar(10)) + ' - '
+ cast(s.SectionId as nvarchar(10)) + ' - '
+ i.Identifier)
from Inserted i
left join MaoNo n
on i.MapNoId = n.MapNoId
left join Section s
on i.SectionId = s.SectionId
where MapLocation.MapNoId = i.MapNoId -- fields here to make sure you update the correct record
End