Xquery的初步學習（一次Lab作業的總結）

Task 1: Open countries.xml, compose the following XQueries:

1. Return the area of Mongolia.

2. Return the names of all cities that have the same name as the country in which they are located.

3. Return the average population of Russian-speaking countries.

4. Returnthenamesofallcountrieswhereover50%ofthepopulationspeaksGerman. (Hint: Dependingonyoursolution, you may want to use ".", which refers to the "current element" within an XPath expression.)

5. Returnthenameofthecountrywiththehighestpopulation. (Hint: Youmayneedtoexplicitlycastpopulationnumbers as integers with xs:int() to get the correct answer.)

第一問：

for $x in doc("countries.xml")/countries/country
where $x/@name="Mongolia"
return <area>{data($x/@area)}</area>

第二問：

for $x in doc("countries.xml")/countries/country
for $y in $x/city
where $y/name= $x/@name
return $y/name 

第三問：

avg(doc("countries.xml")/countries/country[language="Russian"]/@population)

第四問：

for $i in (doc("countries.xml")/countries/country/language[@percentage>50 and .="German"]/../@name)
        return <name>{data($i)}</name>

第五問：

for $x in doc("countries.xml")/countries/country
where $x/@population = max(doc("countries.xml")/countries/country/@population)
return <name>{data($x/@name)}</name>