hive常考SQL題

sql執行順序：from ->  on -> join -> where ->  group by  -> 聚集函數 -> having -> having ->  select  ->distinct -> union -> order by -> limit

（1）分組求最大值

　　1、單表分組最大

//在每一個州中找出最大面積的國家，列出洲份 continent, 國家名字 name 及面積 area
SELECT continent, name, area 
FROM world x
WHERE area >= ALL(    //子查詢相當於查找每一個州的所有area =>笛卡爾乘積，X里的每一個area都會與y的area比較(前提是continent相等)
    SELECT area FROM world y 
　 WHERE y.continent=x.continent
　 AND area>0
)

//有些國家的人口是同洲份的所有其他國的3倍或以上。列出 國家名字name 和 洲份 continent。
SELECT name,continent FROM world x
WHERE x.population / 3 >= ALL(//子查詢相當於找到每州中所有符合的population
    SELECT population FROM world y 
　 WHERE y.continent = x.continent AND population >0 AND y.name != x.name
)

　　2、兩表分組求最大

//每個部門工資最高的員工
方法1
SELECT Department.name AS 'Department',Employee.name AS 'Employee',Salary
FROM Employee JOIN Department ON Employee.DepartmentId = Department.Id
WHERE (Employee.DepartmentId , Salary) IN (
    SELECT 
    DepartmentId, MAX(Salary)
    FROM Employee GROUP BY DepartmentId
)；

方法2
select Department.Name Department,e1.Name Employee,e1.Salary Salary
from Employee e1 join Department on DepartmentId=Department.Id
where Salary >=ALL(
    select Salary
    from Employee e2
    where e1.DepartmentId=e2.DepartmentId
)；

　　3、分組求topN

SQL寫法
SELECT d.Name AS 'Department', e1.Name AS 'Employee', e1.Salary
FROM Employee e1 JOIN Department d ON e1.DepartmentId = d.Id
WHERE 3 > (
    SELECT COUNT(DISTINCT e2.Salary)
    FROM Employee e2
    WHERE e1.Salary < e2.Salary AND e1.DepartmentId = e2.DepartmentId
);

取分組前3的代碼
SELECT e1.Salary
FROM Employee AS e1
WHERE 3 >(
    SELECT count(DISTINCT e2.Salary)
    FROM Employee AS e2
    WHERE e1.Salary <e2.Salary AND e2.DepartmentId = e1.DepartmentId
);

HQL寫法
select name,score
from(
    select name,score,row_number() over(partition by name order by score desc) rank
    from stu_score
)tmp_table
where tmp_table.rank<=3;

（2）利用row_number()和over()分組求topN

select name,score,rank
from (
    select name,score,row_number() over(partition by name order by score desc) rank
    from stu_score
)t
where rank<=3

解析：利用排序函數row_number()和開窗函數over()，其中排序函數row_number()是順序排序，dense_rank()是連續排序，rank()函數是跳躍排序。

（3）利用row_number()和over()求用戶連續登錄最長天數

select uid,max(continuous_days)
from(
    select uid,date_sub(date1-rank),count(1) as continuous_days
    from(
        select uid,date1,row_number() over(partition by uid order by date1) rank
        from user_login
    )
    group by uid,date_sub(date1-rank)
)
group by uid;

解析：其中date_sub(2019-12-31,1)=2019-12-30

（4）求留存率

　　1、先求每天的活躍用戶數，記為A表

select dayNo,count(distinct(uid)) num1
from user_login
group by dayNo

　　2、每天留存數，記為B表

select u.dayNo,count(distinct(s.uid)) num2
from userInfo u1 left join userInfo u2 on u1.uid=u2.uid;
where datediff(u2.dayNo,u1.dayNo)=1
group by u.dayNo

　　3、留層率

select t1.date,t2.num2/t1.num2
from (
    select date,count(distinct(user_id)) num1
    from login 
    group by date
) t1 join (
    select u1.date,count(distinct(u2.user_id)) num2
    from login u1 left join login u2 on u1.user_id=u2.user_id;
    where datediff(u2.date,u1.date)=1
    group by u1.date
) t2 on t1.date=t2.date
union
select date,0.000 as p
from login
where date not in(
　　select t2.date
　　from t2
)

解析：利用A表和B表即可求出哪天的留存率。datediff(2019-12-30,2019-12-31)=1，若求3天留存，則將datediff(2019-12-30,2019-12-31)=3

（5）case when與group by

　　1、利用case when構造多個字段

FName    FCourse    FScore              FName    語文    數學    英語
張三         語文          95.0           張三     95      0       0
張三         數學          80.0           張三     0       80.0    0
張三         英語          70.0    =>     張三     0       0       70
李四         語文          88.0           李四     88.0    0       0           
李四         數學          90.0           李四     0       87.0    0
李四         英語          70.0           李四     0       0       86.0

答案：
FName    語文    數學    英語
張三         95      80      70  
李四         88      87      86
select 
 FName ,
 max(case FCourse when '語文' then FScore else 0 end) as '語文',
 max(case FCourse when '數學' then FScore else 0 end) as '數學',
 max(case FCourse when '英語' then FScore else 0 end) as '英語'
from score
group by FName

　　2、利用case when構造單個字段

解法一：
select FName,
 case 
 when FCourse='數學' then '理科'  else '文科' end as '科別', sum(FScore) as '總分'
from score
group by FName,case when FCourse='數學' then '理科' else '文科' end 
order by FName

解法二
select FName, FType as '科別', sum(FScore) as '總分' 
from (
 select FName, FCourse, FScore, FType = case when FCourse in ('語文','英語') then '文科' else '理科' end 
 from score
) as a
group by FName,FType
order by FName

（6）登錄表：t_login:  user_id,login_time,login_ip，支付表：t_pay:  user_id,pay_time,pay_money

　　1、用1個SQL統計出 登錄總次數、登錄總人數、登錄但未支付的總人數

select count(1),count(distinct a.user_id),
count(distinct case when b.user_id is null then a.user_id end)
from t_login as a left join t_pay as b on a.user_id = b.user_id
或者
select,count1,count2,count(distinct(user_id))
from t_login t3 join (
    select t1.user_id,t2.pay_time,count(login_ip) count1,
    count(distinct(t1.user_id)) count2
    from t_login t1 left join t_pay t2 on t1.user_id=t2.user_id
)t on t.user_id=t3.user_id
where pay_time=null;

　　2、查詢出每個用戶最近的一條登錄數據 user_id，login_time，login_ip

select user_id,login_time,login_ip
(select user_id,login_time,login_ip,
row_number over(partition by user_id order by login_time desc) new_time
from t_login) t
where new_time=1;

　　3、按總支付金額范圍分組統計 支付的總人數、支付的平均金額

select
case
when pay_money >= 1 and pay_money <= 100 then '1~100'
when pay_money >= 101 and pay_money <= 1000 then '101~1000'
when pay_money >= 1001 then '1001+' end pay_limits,
count(distinct(user_id)),
avg(pay_money)
from
t_pay
group by
    case
    when pay_money >= 1 and pay_money <= 100 then '1~100'
    when pay_money >= 101 and pay_money <= 1000 then '101~1000'
    when pay_money >= 1001 then '1001+' end

（7）多表join

　　

select t1.name,t2.name,t3.name
from (city t1 join city t2 on t1.id=t2.parentID) join city t3 on t2.id=t3.parentID

（8）利用explode行轉列

      ===》

  

解析：explode(col_name)：將hive中的一列的array或者map分成多行，如果是字符串類型則利用split將其變成數組；表movie_info與虛表temp_table利用lateral view進行相關聯，其中temp_table表中的字段為category_type

（9）列轉行

　　

　　

   將列表中一個id可能會占用多行轉換為每個user占一行的目標表格式

   

 解析：concat(string1，string2，... )：連接括號內字符串，數量不限；

　　　 concat_ws(separator,string1，string2，... )：連接括號內字符串或者數組，數量不限，連接符為separator。

　　　 collect_set(字段)：此函數只接受基本類型，主要是將字段的值進行去重匯總，產生array類型字段。