Q: add column value to an xml field as an attribute I would like to add an attribute value to an xml field in a query. my example is below
declare @table table (bookid int,xmlCol xml)
insert into @table
select 1,
'<book title="you are not alone" author="Esther">
  <EDITIONS>
    <edition year="2012"/>
    <edition year="2013"/>
  </EDITIONS>
</book>'

declare @table1 table(bookid int,quantity int)
insert into @table1
select 1,3 

select ??? 
from @table t
inner join @table1 t1
on t.bookid = t1.bookid

I want my final result to look like this
<book title="you are not alone" author="Esther" quantity="3">
  <EDITIONS>
    <edition year="2012"/>
    <edition year="2013"/>
  </EDITIONS>
</book>


A: IF you need select data, you can use xquery:
select
    t.xmlCol.query('
         element book {
             for $i in book/@* return $i,
             attribute quantity {sql:column("t1.quantity")},
             for $i in book/* return $i
         }
    ')
from @table t
    inner join @table1 t1 on t.bookid = t1.bookid

sql fiddle demo
or even simplier:
select
    t.xmlCol.query('
         element book {
             book/@*,
             attribute quantity {sql:column("t1.quantity")},
             book/*
         }
    ')
from @table t
    inner join @table1 t1 on t.bookid = t1.bookid

sql fiddle demo

A: If you can use a token in the body of the XML you could use a replace() to replace the token with the quantity value.
declare @table table (bookid int,xmlCol NVARCHAR(MAX))
insert into @table
select 1,
'<book title="you are not alone" author="Esther" {quantity}>
  <EDITIONS>
    <edition year="2012"/>
    <edition year="2013"/>
  </EDITIONS>
</book>'

declare @table1 table(bookid int,quantity int)
insert into @table1
select 1,3 

select 
   CAST(REPLACE(t.xmlCol, '{quantity}', 'quantity="' + CAST(t1.quantity AS NVARCHAR(50)) + '"') AS XML) AS xmlCol
from @table t
inner join @table1 t1
on t.bookid = t1.bookid

Otherwise you could use the xml.modify function like so:
declare @table table (bookid int,xmlCol xml)
insert into @table
select 1,
'<book title="you are not alone" author="Esther">
  <EDITIONS>
    <edition year="2012"/>
    <edition year="2013"/>
  </EDITIONS>
</book>'

declare @table1 table(bookid int,quantity int)
insert into @table1
select 1,3 

DECLARE 
     @myDoc XML
    ,@Qty INT

SET @myDoc = (SELECT xmlCol FROM @table WHERE bookid = 1)
SET @Qty = (SELECT quantity FROM @table1 WHERE bookid = 1)

SET @myDoc.modify('           
insert attribute quantity {sql:variable("@Qty") }           
into   (/book) [1] ') 
SELECT @myDoc

It does not look like you can use the xml.modify in a select statement so you may need to use a loop to loop the vales in table and table1 and write the results to another table for final output. 
