SQL Merge Cells from many rows into a single cell - sql

Question

Similar to the question here:
http://forums.asp.net/t/1580379.aspx/1
I'm trying to merge common cells into a single comma-delimited cell, however across an inner join.
My SQL is:
SELECT DISTINCT tb_Order.OrderNumber, tb_Order.OrderId,
tb_Order.orderDate, tb_Order.OrderTotal,
tb_OrderStatus.OrderStatus, tb_Order.GroupOrderId,
tb_Venue.Title AS Venue
FROM tb_Order INNER JOIN tb_OrderItem ON tb_Order.OrderId = tb_OrderItem.OrderId
INNER JOIN tb_Show ON tb_OrderItem.ShowId = tb_Show.showId
INNER JOIN tb_OrderStatus ON tb_Order.OrderStatusId = tb_OrderStatus.OrderStatusID
INNER JOIN tb_Venue ON tb_Show.VenueId = tb_Venue.id
WHERE (tb_Order.OrderId = 705)
I need the [venue] to be comma-delimited like:
"Interactive Seating Chart Advanced, Interactive Seating Chart Mode Multi-Click"

Answer 1

If you have SQL Server 2017 (14.x) and later, you can use the STRING_AGG function.
SELECT tb_Order.OrderNumber, tb_Order.OrderId,
tb_Order.orderDate, tb_Order.OrderTotal,
tb_OrderStatus.OrderStatus, tb_Order.GroupOrderId,
STRING_AGG(tb_Venue.Title, ',') AS Venue
FROM tb_Order INNER JOIN tb_OrderItem ON tb_Order.OrderId = tb_OrderItem.OrderId
INNER JOIN tb_Show ON tb_OrderItem.ShowId = tb_Show.showId
INNER JOIN tb_OrderStatus ON tb_Order.OrderStatusId = tb_OrderStatus.OrderStatusID
INNER JOIN tb_Venue ON tb_Show.VenueId = tb_Venue.id
WHERE (tb_Order.OrderId = 705)
GROUP BY tb_Order.OrderNumber, tb_Order.OrderId,
tb_Order.orderDate, tb_Order.OrderTotal,
tb_OrderStatus.OrderStatus, tb_Order.GroupOrderId

Answer 2

One way to do this is by using a side effect of row processing order to populate a variable iteratively, like so. The downside of this is that it won't work in a simple query context and it's not the most efficient solution.
DECLARE #venues varchar(max)
SET #venues = ''
SELECT #venues =
CASE WHEN #venues = '' THEN v.Title
ELSE #venues + ',' + v.Title END
FROM tb_Venue v
SELECT #venues
A second way to do this is with STUFF and SQL Server XML extensions, like so:
SELECT DISTINCT v.Title,
(STUFF(
(SELECT ',' + v2.Title
FROM tb_Venue v2
-- uncomment this line if you are going
-- to aggregate only by something in the outer query
-- WHERE v2.GroupKey = v.GroupKey
ORDER BY v2.Title
FOR XML PATH(''), TYPE, ROOT
).value('root[1]','varchar(max)'),1,1,'')) as Aggregation
FROM tb_Venue v
A CLR-based solution is usually the most performant for this use case, and one of those is described here along with a boatload of other less ideal solutions...
Your problem is not one rooted in set logic so there isn't a clean SQL solution...