Explain This Query Please. I Do Not Find About This On Google ,I Want Complete Explaination Of This Query .

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SQL-Server-2008R2

SQL

SELECT Stuff(
  (SELECT N', ' + Name FROM Names FOR XML PATH(''),TYPE)
  .value('text()[1]','nvarchar(max)'),1,2,N'')

stuff is used for replacing by removing a substring
and for xml path is used for getting xml data in a single row but multiple nodes

but i m unable to understand what going on in this
" .value('text()[1]','nvarchar(max)'),1,2,N'') "

my guess is it somehow replaces xml nodes to get comma separated single row data.
but i am confused and i want to understand it all.
please gimme a full explation if its possible.
thank you so much .

Posted 16-Feb-15 23:51pm

varun150

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Umer Akram · Answer 1 · 2015-02-17T02:53:00

your understanding is correct. this is to generate Comma separate value for a list of time.

When FOR XML is used this mean generate the related data in XML.

PATH is a simpler way to define XML element and attributes.

for details please refer FOR XML Path(SQL Server)

So when we use use string concatenation

SELECT N', ' + Name , this means FOR XML will roll up all the values and consider it a single node.

Following code
".value('text()[1]','nvarchar(max)')"

will considered the node value which text()[1] of data type nvarchar(max). you can also use nvarchar(4000).

Consider the following example:

SQL

select 
(Select ', ' + TABLE_NAME
from INFORMATION_SCHEMA.TABLES
FOR XML PATH(''),TYPE).value('text()[1]','nvarchar(4000)')

Hope it help.