Question

I have a table which looks something like

Event ID  Date       Instructor
1         1/1/2000    Person 1
1         1/1/2000    Person 2

Now what I want to do is return this data so that each event is on one row and the Instructors are all in one column split with a <br> tag like 'Person 1 <br> Person 2'

Currently the way I have done this is to use a function

CREATE FUNCTION fnReturnInstructorNamesAsHTML
(
    @EventID INT
)
RETURNS VARCHAR(max)
BEGIN

    DECLARE @Result VARCHAR(MAX)

    SELECT 
        @result = coalesce(@result + '<br>', '') + inst.InstructorName 
    FROM
        [OpsInstructorEventsView]   inst
    WHERE
        inst.EventID = @EventID

    RETURN @result


END

Then my main stored procedure calls it like

   SELECT 
        ev.[BGcolour], 
        ev.[Event] AS name, 
        ev.[eventid] AS ID, 
        ev.[eventstart], 
        ev.[CourseType], 
        ev.[Type], 
        ev.[OtherType], 
        ev.[OtherTypeDesc], 
        ev.[eventend], 
        ev.[CourseNo], 
        ev.[Confirmed], 
        ev.[Cancelled], 
        ev.[DeviceID] AS resource_id, 
        ev.Crew, 
        ev.CompanyName , 
        ev.Notes,
        dbo.fnReturnInstructorNamesAsHTML(ev.EventID) as Names
    FROM 
        [OpsSimEventsView] ev
    JOIN
        [OpsInstructorEventsView]   inst
    ON
        ev.EventID = inst.EventID 

This is very slow, im looking at 4seconds per call to the DB. Is there a way for me to improve the performance of the function? Its a fairly small function so im not sure what I can do here, and I couldnt see a way to work the COALESCE into the SELECT of the main procedure.

Any help would be really appreciated, thanks.

Answer 1

You could try something like this.

SELECT 
    ev.[BGcolour], 
    ev.[Event] AS name, 
    ev.[eventid] AS ID, 
    ev.[eventstart], 
    ev.[CourseType], 
    ev.[Type], 
    ev.[OtherType], 
    ev.[OtherTypeDesc], 
    ev.[eventend], 
    ev.[CourseNo], 
    ev.[Confirmed], 
    ev.[Cancelled], 
    ev.[DeviceID] AS resource_id, 
    ev.Crew, 
    ev.CompanyName , 
    ev.Notes,
    STUFF((SELECT '<br>'+inst.InstructorName
           FROM [OpsInstructorEventsView]   inst
           WHERE ev.EventID = inst.EventID
           FOR XML PATH(''), TYPE).value('.', 'nvarchar(max)'), 1, 4, '') as Names
FROM 
    [OpsSimEventsView] ev

Not sure why you have joined OpsInstructorEventsView in the main query. I removed it here but if you needed you can just add it again.