跟著CodeQL官方的QL tutorials做練習，在Crown the rightful heir這一章節(jié)中有五個問題，來做一做。在看這篇文章之前需先跟著官方的QL tutorial做一遍。

下面的CodeQL代碼，直接放到這里運行即可

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

第一個問題：村里發(fā)色最多的一種是哪種顏色

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()

執(zhí)行結果：

brown   46

第二個問題：每個地區(qū)發(fā)色最多的一種是哪種顏色

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)

執(zhí)行結果：

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

說明下：各地區(qū)擁有brown發(fā)色的人的個數分別是：

• 西部：7
• 東部：11
• 北部：3
• 南部：10
• 無地區(qū)：15 （也就是Person.getLocation()為空的人）

總數就是46，符合第一個問題的查詢結果。

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

第一個問題：哪位村民擁有最多小孩

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)

第二個問題：哪位村民擁有最多后代

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?

各地區(qū)分別有多少人居住：

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)

（查詢結果不包含20位無地區(qū)的人員）

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

找出跟他家長不住在同一地區(qū)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.)

這個問題不太具體，我理解為：找出比他后代的年紀還小的人。

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()