1. 1 XQuery Slides From Dr. Suciu

2. 2 XQuery Based on Quilt, which is based on XML-QL Uses XPath to express more complex queries

3. 3 Xpath: Summary bibmatches a bib element *matches any element /matches the root element /bibmatches a bib element under root bib/papermatches a paper in bib bib//papermatches a paper in bib, at any depth //papermatches a paper at any depth paper|bookmatches a paper or a book @pricematches a price attribute bib/book/@pricematches price attribute in book, in bib

4. 4 FLWR (“Flower”) Expressions FOR... LET... WHERE... RETURN... FOR... LET... WHERE... RETURN...

5. 5 Addison-Wesley Serge Abiteboul Rick Hull Victor Vianu Foundations of Databases 1995 Freeman Jeffrey D. Ullman Principles of Database and Knowledge Base Systems 1998 Addison-Wesley Serge Abiteboul Rick Hull Victor Vianu Foundations of Databases 1995 Freeman Jeffrey D. Ullman Principles of Database and Knowledge Base Systems 1998 Sample Data for Queries (more or less)

6. 6 FOR-WHERE-RETURN Find all book titles published after 1995: for $x in doc("bib.xml")/bib/book where data($x/@year) > 1999 return $x/title for $x in doc("bib.xml")/bib/book where data($x/@year) > 1999 return $x/title Result: abc def ghi

7. 7 FOR-WHERE-RETURN Equivalently (perhaps more geekish) FOR $x IN doc("bib.xml")/bib/book[@year > 1995] /title RETURN $x FOR $x IN doc("bib.xml")/bib/book[@year > 1995] /title RETURN $x And even shorter: doc("bib.xml")/bib/book[@year > 1995] /title

8. 8 FOR-WHERE-RETURN Find all book titles and the year when they were published: FOR $x IN doc("bib.xml")/bib/book RETURN { $x/title/text() } { $x/year/text() } We can construct whatever XML results we want !

9. 9 Answer How to cook a Turkey 2003 Cooking While Watching TV 2004 Turkeys on TV 2002.....

10. 10 FOR-WHERE-RETURN Notice the use of “{“ and “}” What is the result without them ? FOR $x IN doc("bib.xml")/bib/book RETURN $x/title/text() $x/year/text()

11. 11 XQuery: Nesting For each author of a book by Morgan Kaufmann, list all books she published: FOR $b IN doc(“bib.xml”)/bib, $a IN $b/book[publisher /text()=“Morgan Kaufmann”]/author RETURN { $a, FOR $t IN $b/book[author/text()=$a/text()]/title RETURN $t } FOR $b IN doc(“bib.xml”)/bib, $a IN $b/book[publisher /text()=“Morgan Kaufmann”]/author RETURN { $a, FOR $t IN $b/book[author/text()=$a/text()]/title RETURN $t }

12. 12 XQuery Jones abc def Smith ghi Jones abc def Smith ghi Result:

13. 13 Inverting Hierarchy { for $p in distinct-values(doc("bib.xml")//publisher) order by $p return { $p } { for $b in doc("bib.xml")/bib/book where $b/publisher = $p order by $b/title return $b/title } }

14. 14 Aggregates Find all books with more than 3 authors: count = a function that counts avg = computes the average sum = computes the sum distinct-values = eliminates duplicates FOR $x IN doc("bib.xml")/bib/book WHERE count($x/author)>3 RETURN $x for $l in distinct-values(doc("bib.xml")//author/last) return { $l } for $l in distinct-values(doc("bib.xml")//author/last) return { $l }

15. 15 Aggregates { for $b in doc("books.xml")//book let $c := $b/author return { $b/title, { count($c) } } }

16. 16 XQuery Find books whose price is larger than average: { for $b in doc("bib.xml")/bib let $a := avg($b/book/price/text()) for $x in $b/book where ($x/price/text() > $a) return $x } { for $b in doc("bib.xml")/bib let $a := avg($b/book/price/text()) for $x in $b/book where ($x/price/text() > $a) return $x } LET binds a variable to one value; FOR iterates a variable over a list of values

17. 17 FOR v.s. LET FOR $x IN /bib/book RETURN { $x } FOR $x IN /bib/book RETURN { $x } Returns:... LET $x := /bib/book RETURN { $x } LET $x := /bib/book RETURN { $x } Returns:...

18. 18 For vs Let (cont’d) for $i in (1, 2, 3) let $j := "a" return { $i } { $j } for $i in (1, 2, 3), $j in (4, 5, 6) return { $i } { $j }

19. 19 SQL and XQuery Side-by-side Product(pid, name, maker, price) Find all product names, prices, sort by price SELECT x.name, x.price FROM Product x ORDER BY x.price SQL FOR $x in doc(“db.xml”)/db/Product/row ORDER BY $x/price/text() RETURN { $x/name, $x/price } XQuery

20. 20 abc 7 def 23.... Answers Notice: this is NOT a well-formed document ! (WHY ???) NamePrice abc7 def23...

21. 21 Producing a Well-Formed Answer { FOR $x in doc(“db.xml”)/db/Product/row ORDER BY $x/price/text() RETURN { $x/name, $x/price } }

22. 22 abc 7 def 23.... Xquery’s Answer Now it is well-formed !

23. 23 SQL and XQuery Side-by-side Product(pid, name, maker, price) Company(cid, name, city, revenues) Find all products made in Seattle SELECT x.name FROM Product x, Company y WHERE x.maker=y.cid and y.city=“Seattle” SQL FOR $r in doc(“db.xml”)/db, $x in $r/Product/row, $y in $r/Company/row WHERE $x/maker/text()=$y/cid/text() and $y/city/text() = “Seattle” RETURN { $x/name } XQuery FOR $y in /db/Company/row[city/text()=“Seattle”], $x in /db/Product/row[maker/text()=$y/cid/text()] RETURN { $x/name } Cool XQuery

24. 24 123 abc efg …. ….......

25. 25 SQL and XQuery Side-by-side For each company with revenues < 1M count the products over $100 SELECT y.name, count(*) FROM Product x, Company y WHERE x.price > 100 and x.maker=y.cid and y.revenue < 1000000 GROUP BY y.cid, y.name FOR $r in doc(“db.xml”)/db, $y in $r/Company/row[revenue/text() { $y/name/text() } { count($r/Product/row[maker/text()=$y/cid/text()][price/text()>100]) }

26. 26 SQL and XQuery Side-by-side Find companies with at least 30 products, and their average price SELECT y.name, avg(x.price) FROM Product x, Company y WHERE x.maker=y.cid GROUP BY y.cid, y.name HAVING count(*) > 30 FOR $r in doc(“db.xml”)/db, $y in $r/Company/row LET $p := $r/Product/row[maker/text()=$y/cid/text()] WHERE count($p) > 30 RETURN { $y/name/text() } avg($p/price/text()) A collection An element

27. 27 FOR v.s. LET FOR Binds node variables  iteration LET Binds collection variables  one value

28. 28 XQuery Summary: FOR-LET-WHERE-RETURN = FLWR FOR/LET Clauses WHERE Clause RETURN Clause List of tuples Instance of Xquery data model