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I have a temp table that will contain two columns ID and Text. The temp table will contain an unknown amount of rows but there will always be an even amount. What I need to do is select every other row starting at 0 (so 0, 2, 4, 6, etc.) and then concatenate the values of Text together. I found http://stackoverflow.com/questions/4799816/return-row-of-every-nth-record which looks to be how to get every other row but I am not sure how to do the concatenation.

Example Table:

Row ID Text
0   0  This
1   1  Do
2   2  is
3   3  not
4   4  the
5   5  use
6   6  text
7   7  text

The result I would want from that table is This is the text.

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2 Answers 2

up vote 3 down vote accepted
DECLARE @x TABLE(ID INT, [Text] NVARCHAR(32));

INSERT @x VALUES (0,N'This'), (1,N'Do'),  (2,N'is'),   (3,N'not'), 
                 (4,N'the'),  (5,N'use'), (6,N'text'), (7,N'text');

SELECT LTRIM((SELECT ' ' + [Text] FROM 
  (SELECT rn = ROW_NUMBER() OVER (ORDER BY ID), [Text] FROM @x) AS x(rn, [Text])
  WHERE rn % 2 = 1 ORDER BY rn FOR XML PATH, TYPE).value('.[1]','nvarchar(max)'));

Result:

This is the text

If you know your strings can't contain characters like <, > and & then it should be slightly more efficient to leave out the TYPE).value bit:

SELECT LTRIM((SELECT ' ' + [Text] FROM 
  (SELECT rn = ROW_NUMBER() OVER (ORDER BY ID), [Text] FROM @x) AS x(rn, [Text])
  WHERE rn % 2 = 1 ORDER BY rn FOR XML PATH('')));
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Can you explain what FOR XML PATH, TYPE).value('.[1]','nvarchar(max)'),1,1,''); does and it's purpose? –  user11512 Oct 14 '13 at 14:35
2  
FOR XML PATH is described lightly here and here. Essentially, it's a way to trick XML into performing string concatenation for us, but in a defined way (hence the ORDER BY). The TYPE).value stuff is just protection against strings like 'hey<man' from messing up the XML formatting, < is also a special XML character. –  Aaron Bertrand Oct 14 '13 at 14:39

Try this

declare @tTable TABLE(ID INT identity, tText nvarchar(100));
declare @tString nvarchar(4000);

insert into @tTable VALUES
('This'),
('Do'),
('is'),
('not'),
('the'),
('use'),
('text'),
('text')

select @tString = COALESCE(@tString+' ','') + tText
from @tTable
where id%2 = 1

select @tString
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3  
This approach isn't guaranteed to concatenate them in the correct order. Or to work at all in fact –  Martin Smith Oct 14 '13 at 14:11
    
This worked perfectly and is much cleaner then the post I had linked to thanks. –  user11512 Oct 14 '13 at 14:15
5  
@MatthewVerstraete Please see the many quotes from Microsoft I compiled on the previous link. Even without ORDER BY, we do not guarantee that @var = @var + will produce the concatenated value for any statement that affects multiple rows. The right-hand side of the expression can be evaluated either once or multiple times during query execution and the behavior as I said is plan dependent. –  Martin Smith Oct 14 '13 at 14:16
2  
@Matthew it may look cleaner but it is not guaranteed to work. –  Aaron Bertrand Oct 14 '13 at 14:18
2  
Ok in light of all the comments I have unmarked the answer and will now be testing @AaronBertrand post –  user11512 Oct 14 '13 at 14:36

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