How to SELECT DISTINCT with an ORDER BY and FOR XML in SQL Server 2008+

Question

So I have been fighting with this for a while now and I thought this had to be a simple task. My goal is to return a single string of all the unique rows returned separated with a forward slash and ordered by the time they were entered. Here is example data

Table: Locations

Location   Time
========   =======
OR1        2013-02-06 16:55:47.000
OR1        2013-02-06 16:56:34.000
ICU1       2013-02-06 16:59:50.000
OR1        2013-02-06 17:02:50.000
ICU1       2013-02-06 17:09:50.000

So given the above table of data I want to return a string that says this "OR1/ICU1". I can return the distinct values as a string using FOR XML PATH but as soon as I throw in the ORDER BY it all falls apart with errors.

Ideas?

Answer 1

Try that;

SELECT STUFF ((
  SELECT cast('/' as Varchar(max)) + Location
     From Locations
     Group by Location
     Order by MAX(Time) FOR XML PATH('')) , 1 , 1 , '' ) as result

Answer 2

Use a temporary table in your query, and a while loop, but I would not recommend doing so against large production data whose performance may be negatively impacted.

For example.

/*Create our temp table */
DECLARE @MyTemp TABLE (Location VARCHAR(10), Processed BIT DEFAULT 0)

/*Load the temp table will all the distinct locations */    
INSERT INTO @MyTemp SELECT DISTCINT Location FROM Locations

/* need these variable to hold data */    
DECLARE @FinalString VARCHAR(1000) = ''
DECLARE @Location VARCHAR(10) = ''

/*as long as there is any row with an unprocessed location in the table 
we want to continue this process */
WHILE EXISTS(SELECT 1 FROM @MyTemp WHERE Processed = 0)
BEGIN
     /* Grab our next unprocessed location */
     SELECT TOP 1 @Location = Location FROM @MyTemp WHERE Processed = 0 ORDER BY Location
     /* Add it to the final string */
     SET @FinalString = @FinalString + '/' + @Location
     /* mark the location as processed */
     UPDATE @MyTemp SET Processed = 1 WHERE Location = @Location
END

/* get the final result (note this will have a leading '/') */
SELECT @FinalString