Inner select on one to many

Question

Hi all,

I have 2 tables event + event_artist

event
eventId | eventName
1 , gig1
2, gig2

event_artist
eventId, artistName
1, Led Zip
1, The Beatles

ie Led Zep and the Beatles are both playing @ Gig1

I need to create the SQl to bind to a gridview ( you necessarily need to know about gridviews to answers this )

The results that i want would look like this eventId = 1, EventName = Gig1. ArtistLineup = Led Zep, The beatles

So i need to create an alias ArtistLineup that would list all the artist. Via an inner select i think.

Any thoughts on what this would look like.

Answer 1

SQL Server doesn't have anything built in to concatenate values in one statement like that. You could build the strings, but it has to be done one at a time.

However, you can get around this by building your own custom aggregate function (requires messy games with ActiveX objects in SQL Server 2000)

Answer 2

you might want to try something like this: http://stackoverflow.com/questions/279444/why-does-this-sql-script-work-as-it-does

Answer 3

Saw this in SQL Server Magazine- not great, and the total list will have an upper length limit, but:

drop table event
go

drop table event_artist
go

create table event (eventid int, eventname varchar(255))
go

create table event_artist (eventid int, artistname varchar(255))
go

insert into event values (1, 'gig1')
go

insert into event values (2, 'gig2')
go

insert into event_artist values (1, 'Led Zip')
go

insert into event_artist values (1, 'The Beatles')
go

drop function Event_Display
go

create function Event_Display (@EventID int) returns varchar(2000) as
begin
    declare @artistList varchar(2000)
    set @artistList=''

    select @artistList=@artistList + ', ' + isnull(artistname,'') 
    from event_artist 
    where eventid=@EventID

    return substring(@artistList,3,2000)  --eliminate initial comma
end
go

select event.eventid, event.eventname, dbo.Event_Display(event.eventid) from event

                                                                                                                                                                                                                                                   
1           gig1        Led Zip, The Beatles

2           gig2     

Answer 4

ScottK's answer is basically the one you want. Here's the rest of mine:

The query: select e.*, dbo.ArtistList(e.EventId) as ArtistList from [event] e

The function:
CREATE FUNCTION ArtistList
(
-- Add the parameters for the function here
@EventId int
)
RETURNS varchar(MAX)
AS
BEGIN
-- Declare the return variable here DECLARE @ArtistList varchar(MAX)

-- Add the T-SQL statements to compute the return value here
SELECT @ArtistList = COALESCE(@ArtistList + ', ', '') + Artist
FROM EventArtist
WHERE EventId = @EventId

-- Return the result of the function
RETURN @ArtistList

END
GO

The only difference between my answer and ScottK's you might take note of is my use of varchar(MAX). That should pretty much address any concerns about the list of artists being truncated.

I've deleted my previous (incomplete) answer.

Answer 5

You can use the clever FOR XML trick posted by Kevin Fairchild (I've modified it to take account of band names which will include spaces):

/*
create table [event] (eventid int, eventname varchar(255))
create table event_artist (eventid int, artistname varchar(255))
insert into [event] values (1, 'gig1')
insert into [event] values (2, 'gig2')
insert into event_artist values (1, 'Led Zip')
insert into event_artist values (1, 'The Beatles')
*/

SELECT  e.eventid
       ,e.eventname
       ,REPLACE(REPLACE(RTRIM((
                               SELECT   artistname + '| '
                               FROM     [event_artist]
                               WHERE    eventid = e.eventid
                              FOR
                               XML PATH('')
                              )), '| ', ', '), '|', '') AS artists
FROM    [event] AS e

Note that this requires columns in the FOR XML to be unnamed (named columns get an XML wrapper).