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TSQL - Removing a trailing comma from a list of concatenated values

On a semi-regular basis I'd need to squish a list of comma-delimited values all concatenated together into one field, so I'd use this old snippet:

SELECT LEFT(ConcatValues, LEN(ConcatValues)-1) AS 'TheValues'
FROM SomeTable t
      CROSS APPLY ( SELECT    t2.SomeField + ', ' AS [text()]
                    FROM      SomeTable t2
                    WHERE     t.SomeField = t2.SomeField

                    FOR XML PATH('') ) C (ConcatValues)

Problem is when the concatenated field has length zero, LEFT gets a -1 length and returns an error:

Msg 537, Level 16, State 5, Line 1
Invalid length parameter passed to the LEFT or SUBSTRING function.

So today I had a look around and found a better way from this StackOverflow thread. Just replace the LEFT function with this:

STUFF(ConcatValues, LEN(ConcatValues), 1, '')

It gives the exact same results except that the STUFF function is way more tolerant of being given inappropriate length parameters and just returns NULL (which is exactly what I want) instead of throwing errors.  From the MSDN documentation:

"If the start position or the length is negative, or if the starting position is larger than length of the first string, a null string is returned. If the start position is 0, a null value is returned. If the length to delete is longer than the first string, it is deleted to the first character in the first string"

Comments

  1. Within your existing SELECT:

    STUFF((SELECT ', ' + table.withmultiplevalues AS [text()]
    FROM dbo.locationoflist table
    WHERE table.fromouterselect = table.relatingvalue
    FOR XML PATH('')
    ), 1, 1, '' )
    AS [name of conclist]

    ReplyDelete
    Replies
    1. Huh, that's pretty cool! This would definitely work better inline in a SELECT since rather than having the "conclist" referring to the CROSS APPLY which is possibly several scrolls down, you could put the whole lot in one place... Much easier to read!

      Delete

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