Update XML with value from another (non-xml) column in T-SQL - sql

Question

I have a table with two fields of type NUMERIC and one field of type XML. Here is a rough sample:
CREATE TABLE books (
ID INT NOT NULL,
price NUMERIC(4,2),
discount NUMERIC(2,2),
book XML
);
The XML value will look something like, say,
<?xml version="1.0" encoding="UTF-8"?>
<book>
<title>Harry Potter</title>
<author>J K Rowling</author>
<Store>
<Name>Burke and Burkins</Name>
<Address>Some St, Somewhere, Some City</Address>
</Store>
</book>
Now my question is, using xml.modify(), how can I add two xpaths under Store with the price and discount with value from books.price and books.discount?
<?xml version="1.0" encoding="UTF-8"?>
<book>
<title>Harry Potter</title>
<author>J K Rowling</author>
<Store>
<Name>Burke and Burkins</Name>
<Address>Some St, Somewhere, Some City</Address>
<Price>value from books.price from the same row</Price>
<Discount>value from books.discount from the same row</Discount>
</Store>
</book>
This is a rough example, so please don't worry about where the XML data came from. Lets just say the book column has the XML data already present.
I know how to update the table with static values with,
UPDATE books
SET book.modify('insert <Price>10.99</Price><Discount>20.00</Discount> after (/book/Store/Address)[1]')
Performance is not a consideration here.

Answer 1

It is not possible to do two modifications in one statement.
In this case you might trick this out by first combining both values and then insert them at once.
I use an updateable CTE to achieve this:
CREATE TABLE books (
ID INT NOT NULL,
price NUMERIC(4,2),
discount NUMERIC(2,2),
book XML
);
--Fill the table with data
INSERT INTO books VALUES(1,10.5,.5,
'<book>
<title>Harry Potter</title>
<author>J K Rowling</author>
<Store>
<Name>Burke and Burkins</Name>
<Address>Some St, Somewhere, Some City</Address>
</Store>
</book>');
--This is the actual query
WITH CTE AS
(
SELECT *
,(SELECT price AS Price,discount AS Discount FOR XML PATH(''),TYPE) AS XmlNode
FROM books
)
UPDATE CTE SET book.modify('insert sql:column("XmlNode") after (/book/Store/Address)[1]');
--Check the result
SELECT *
FROM books;
--Clean-Up (carefull with real date!)
GO
--DROP TABLE books;
One hint
Your XML column, if it is really XML, will - for sure! - not contain an XML starting with <?xml version="1.0" encoding="UTF-8"?>. The internal encoding is always unicode (ucs-2, which is almost utf-16) and one cannot change this. If you pass in a declaration, it is either ommited or you'll get an error.
UPDATE
Another approach was to first read the XML's values and then to rebuild it:
WITH CTE AS
(
SELECT *
,(SELECT b.value('title[1]','nvarchar(max)') AS [title]
,b.value('author[1]','nvarchar(max)') AS [author]
,b.value('(Store/Name)[1]','nvarchar(max)') AS [Store/Name]
,b.value('(Store/Address)[1]','nvarchar(max)') AS [Store/Address]
,price AS [Store/Price]
,discount AS [Store/Discount]
FROM book.nodes('book') AS A(b)
FOR XML PATH('book'),TYPE
) AS bookNew
FROM books
)
UPDATE CTE SET book=bookNew;