跟着CodeQL官方的QL tutorials做练习，在Crown the rightful heir这一章节中有五个问题，来做一做。在看这篇文章之前需先跟着官方的QL tutorial做一遍。

下面的CodeQL代码，直接放到这里运行即可

What is the most common hair color in the village? And in each region?

第一个问题：村里发色最多的一种是哪种颜色

import tutorial

class HairColor extends string{
  HairColor(){
    exists(Person p | this = p.getHairColor())
  }
  
  int ct(){
    result = count(Person p | p.getHairColor() = this | p)
  }
  
}


from HairColor c
where not exists(HairColor c1 | c1.ct() > c.ct())
select c, c.ct()

执行结果：

brown	46

第二个问题：每个地区发色最多的一种是哪种颜色

import tutorial

class HairColor extends string{
  HairColor(){
    exists(Person p | this = p.getHairColor())
  }
  
  // int ct(){
  //   result = count(Person p | p.getHairColor() = this | p)
  // }
  
  int ctOfLocation(Location loc){ 
    result = count(Person p | p.getLocation() = loc and p.getHairColor() = this | p)
  }
}

class Location extends string{
  Location() {
    this in ["east", "west", "south", "north"]
  }
}

from Location location, HairColor c
where c.ctOfLocation(location) = max(HairColor c1 | | c1.ctOfLocation(location) )
select location, c, c.ctOfLocation(location)

执行结果：

west	brown	7
east	brown	11
north	black	8
south	brown	10

说明下：各地区拥有brown发色的人的个数分别是：

• 西部：7
• 东部：11
• 北部：3
• 南部：10
• 无地区：15 （也就是Person.getLocation()为空的人）

总数就是46，符合第一个问题的查询结果。

Which villager has the most children? Who has the most descendants?

第一个问题：哪位村民拥有最多小孩

import tutorial

Person childOf(Person p) {
  p = parentOf(result)
}

int childrenNumber(Person p) {
  result = count(Person c | c = childOf(p) | c)
}

from Person p
where childrenNumber(p) = max(Person q | | childrenNumber(q))
select p, childrenNumber(p)

第二个问题：哪位村民拥有最多后代

import tutorial

Person descendantOf(Person p) {
  p = parentOf+(result)
}

int descendantNumber(Person p) {
  result = count(Person c | c = descendantOf(p) | c)
}

from Person p
where descendantNumber(p) = max(Person q | | descendantNumber(q))
select p, descendantNumber(p)

How many people live in each region of the village?

各地区分别有多少人居住：

import tutorial


class Location extends string{
  Location() {
    this in ["east", "west", "south", "north"]
  }
}

from Location location
select location, count(Person p |  p.getLocation() = location | p)

（查询结果不包含20位无地区的人员）

Do all villagers live in the same region of the village as their parents?

找出跟他家长不住在同一地区的人：

import tutorial


from Person p, Person c
where p = parentOf(c) and p.getLocation() != c.getLocation()
select c

Find out whether there are any time travelers in the village! (Hint: Look for “impossible” family relations.)

这个问题不太具体，我理解为：找出比他后代的年纪还小的人。

import tutorial

Person descendantOf(Person p) {
  p = parentOf+(result)
}

from Person p
where exists(Person c | c = descendantOf(p) and p.getAge() < c.getAge())
select p, p.getAge()