Comments on: Not-so-dirty SQL hacks

By: merrillaldrich

merrillaldrich — Wed, 18 Sep 2013 02:49:20 +0000

Rob – I don’t have to code much. We buy everything. If I had to code this I would probably cringe and write it as you show here. It’s become sort of a best practice, but it’s still not pretty :-).

By: Allan S. Hansen

Allan S. Hansen — Tue, 17 Sep 2013 08:52:14 +0000

I’ve used XML for string concat in SQL Server for a couple of years now, and it’s always felt ‘hacky’ – but – yes, it really does the trick.
I rarely – however – put it into production code other than data migration or imports which aren’t that time sensitive.
In other situations, I’d properly rather handle it with a combination of database/code logic as string concatenation often is connection to a business logic problem needing to be solved, more than an actual data problem.

By: Josías Hernández

Josías Hernández — Mon, 16 Sep 2013 18:32:26 +0000

It is just AWESOME !!! I really enjoy it !!! Very smart the solution!!!
Thanks for the trick Rob.

By: Rob Farley

Rob Farley — Thu, 12 Sep 2013 23:50:47 +0000

How do you handle it then, Merrill?

By: merrillaldrich

merrillaldrich — Thu, 12 Sep 2013 19:00:44 +0000

I’m crazy and self-destructive, I guess. I know the performance advantages. I get the reasoning.
AND … still I cringe when I see this XML concatenation trick. It’s my childish idealism.
Still, great explanation of how to do it :-).

By: Rob Farley

Rob Farley — Thu, 12 Sep 2013 16:25:26 +0000

Based on the fact that it’s not supported.
Based on the fact that it can be affected by non-clustered indexes, parallelism, and other good things, giving ‘incorrect’ results.
Based on the fact that it’s procedural and has no opportunity to be handled by the QO in a better way.
Based on the fact that you can’t order the data how you like without risking the results.
If you must use code that moves through a result set in order like that, you should use a cursor. And that’s saying something!!

By: JDS

JDS — Thu, 12 Sep 2013 16:13:40 +0000

I have always done something like this below for quick string concatenation. Do you prefer the XML based approach upon performance or some other criteria?
IF EXISTS ( SELECT *
FROM tempdb.dbo.sysobjects
WHERE ID = OBJECT_ID(N’tempdb..#source’) )
BEGIN
DROP TABLE #source
END
CREATE TABLE #source (
col1 CHAR(1)
)
INSERT INTO #source
(col1)
VALUES (‘a’)
, (‘b’)
, (‘c’)
, (‘d’)
, (‘e’)
, (‘f’)
, (‘g’)
/*******************
String Concatenation
********************/
DECLARE @string VARCHAR(MAX)
SELECT @string = ISNULL(@string,”) + ‘,’ + col1
FROM #source s
SELECT @string