1 XQuery Slides From Dr. Suciu

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

3 FOR-WHERE-RETURN Find all book titles published after 1995: for $x in doc("bib.xml")/bib/book where > 1999 return $x/title for $x in doc("bib.xml")/bib/book where > 1999 return $x/title Result: abc def ghi doc(“bib.xml”) in freexml editor by default looks for bib.xml in the default directory where it was installed

4 FOR-WHERE-RETURN Equivalently (perhaps more geekish) FOR $x IN > 1995] /title RETURN $x FOR $x IN > 1995] /title RETURN $x And even shorter: > 1995] /title

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

6 Answer TCP/IP Illustrated 1994 Advanced Programming in the UNIX Environment 1992 Data on the Web 2000 The Economics of Technology and Content for Digital TV 1999 TCP/IP Illustrated 1994 Advanced Programming in the UNIX Environment 1992 Data on the Web 2000 The Economics of Technology and Content for Digital TV 1999

7 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()

8 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 }

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

10 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

11 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:...

12 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 } for $i in (1, 2, 3) let $j := ( 4 to 6) return { $i } { $j }

13 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 }

14 XQuery Jones abc def Smith ghi Jones abc def Smith ghi Result:

15 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 } } List of titles published by each publisher

16 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

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

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

19 abc 7 def Xquery’s Answer Now it is well-formed !

20 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

abc efg …. …

22 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 < 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]) }

23 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