XQuery wont return a document - sql

Question

I just started learning about XQuery and am trying to play with it a little.
Now, iv'e built what i think is a simple query and a correct one (a much as i can see) but SQL Manger
prints me the error:
XQuery [query()]: "=" was expected.
I looked back at the code but i cant understand how to fix it..
here is my code:
DECLARE #x AS XML = N'
<bookstore>
<book category="cooking">
<title lang="en">Everyday Italian</title>
<author>Giada De Laurentiis</author>
<year>2005</year>
<price>30.00</price>
</book>
<book category="children">
<title lang="en">Harry Potter</title>
<author>J K. Rowling</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="web">
<title lang="en">XQuery Kick Start</title>
<author>James McGovern</author>
<author>Per Bothner</author>
<author>Kurt Cagle</author>
<author>James Linn</author>
<author>Vaidyanathan Nagarajan</author>
<year>2003</year>
<price>49.99</price>
</book>
<book category="web" cover="paperback">
<title lang="en">Learning XML</title>
<author>Erik T. Ray</author>
<year>2003</year>
<price>39.95</price>
</book>
</bookstore>';
SELECT #x.query('for $i in bookstore/book
let $a := $i/author
let $t := $i/title
let $p := $i/price
where $i/#price < 40
return
<This is a test>
<author>$a</author>
<title>$t</title>
<price>$p</price>
</This is a test>')
AS [I hope this works]
Thanks in advance for your help :)

Answer 1

This is not a valid xml element:
<This is a test>
changing this to
<ThisIsATest>
will fix your query but after the fix, as-is, your query doesn't return anything. My T-SQL XQuery skills are rusty but you can get what you're trying to do using nodes and the values method.
This:
SELECT
author = bs.book.value('(author/text())[1]', 'varchar(8000)'),
title = bs.book.value('(title/text())[1]', 'varchar(8000)'),
price = bs.book.value('(price/text())[1]', 'varchar(8000)')
FROM (VALUES(#x)) AS ml(x)
CROSS APPLY ml.x.nodes('bookstore/book') AS bs(book);
Returns:
author title price
--------------------- --------------------- ----------
Giada De Laurentiis Everyday Italian 30.00
J K. Rowling Harry Potter 29.99
James McGovern XQuery Kick Start 49.99
Erik T. Ray Learning XML 39.95
This (which includes your sample XML):
DECLARE #x AS XML = N'
<bookstore>
<book category="cooking">
<title lang="en">Everyday Italian</title>
<author>Giada De Laurentiis</author>
<year>2005</year>
<price>30.00</price>
</book>
<book category="children">
<title lang="en">Harry Potter</title>
<author>J K. Rowling</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="web">
<title lang="en">XQuery Kick Start</title>
<author>James McGovern</author>
<author>Per Bothner</author>
<author>Kurt Cagle</author>
<author>James Linn</author>
<author>Vaidyanathan Nagarajan</author>
<year>2003</year>
<price>49.99</price>
</book>
<book category="web" cover="paperback">
<title lang="en">Learning XML</title>
<author>Erik T. Ray</author>
<year>2003</year>
<price>39.95</price>
</book>
</bookstore>';
SELECT
author = bs.book.value('(author/text())[1]', 'varchar(8000)'),
title = bs.book.value('(title/text())[1]', 'varchar(8000)'),
price = bs.book.value('(price/text())[1]', 'varchar(8000)')
FROM (VALUES(#x)) AS ml(x)
CROSS APPLY ml.x.nodes('bookstore/book') AS bs(book)
FOR XML PATH('Book');
Returns:
<Book>
<author>Giada De Laurentiis</author>
<title>Everyday Italian</title>
<price>30.00</price>
</Book>
<Book>
<author>J K. Rowling</author>
<title>Harry Potter</title>
<price>29.99</price>
</Book>
<Book>
<author>James McGovern</author>
<title>XQuery Kick Start</title>
<price>49.99</price>
</Book>
<Book>
<author>Erik T. Ray</author>
<title>Learning XML</title>
<price>39.95</price>
</Book>

Answer 2

You were close, but there are three things to mention:
As Alan Burstein has told you, the tag <This is a test> is not valid. The message you get, is because the engine thinks of an element <This> and expects the is to be the first attribute, which should be followed by = like in <This is="some value">.
Your where tries to query a #price attribute
In order to resolve the values you need {} around your variables.
Try this:
SELECT #x.query('for $i in bookstore/book
let $a := $i/author
let $t := $i/title
let $p := $i/price
where $p < 40
return
<This-is-a-test>
<author>{$a}</author>
<title>{$t}</title>
<price>{$p}</price>
</This-is-a-test>')
AS [I hope this works]