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