【Hive】学习与优化3（含常用面试题）

 

• hive size计算数组长度

hive上有个表，其中某列p_9的数据格式是用逗号分隔的字符串。通过下面的方式计算p_9列使用逗号分隔后元素的长度。

select rg,sum(size(split(p_9,","))) from ttengine_api_data where dt='2017-08-07' group by rg;
 
OK
0	137683
1	150155

如果p_9列不为空，那么计算是没问题的。如果是空（“”或者null），则计算后是有问题的。仔细查了一下，发现是size(split(p_9,",")) 有问题，即：
如果p_9是空或者null，那么split成数组后，在计算数据的长度居然是1。知道了原因，那么改起来很简单，使用下面的方式统计就没问题了：

select rg,sum(if(length(p_9)==0,0,size(split(p_9,",")))) from ttengine_api_data where dt='2017-08-07' group by rg;
OK
0	0
1	6373
 

• HiveQL实现累积求和

有如下访客访问次数的统计表 t_access

访客  月份  访问次数  
A   2015-01 5  
A   2015-01 15  
B   2015-01 5  
A   2015-01 8  
B   2015-01 25  
A   2015-01 5  
A   2015-02 4  
A   2015-02 6  
B   2015-02 10  
B   2015-02 5  
……  ……  ……  

要求输出每个客户在每个月的总访问次数，以及在当前月份之前所有月份的累积访问次数。

输出表

访客  月份      月访问总计   累计访问总计  
A   2015-01        33          33  
A   2015-02        10          43  
……. ……. ……. ……. ……. ……. ……. …….  ……. …….  
B   2015-01        30          30  
B   2015-02        15          45  
……. ……. ……. ……. ……. ……. ……. …….  ……. …….   

【解析】

 1）第一步，先求每个用户的月总访问次数

select username,month,sum(count) as salary from t_access_times group by username,month

+-----------+----------+---------+--+  
| username  |  month   | count   |  
+-----------+----------+---------+--+  
| A         | 2015-01  | 33      |  
| A         | 2015-02  | 10      |  
| B         | 2015-01  | 30      |  
| B         | 2015-02  | 15      |  
+-----------+----------+---------+--+  

2）第二步，将月总访问次数表 自己连接 自己连接(内连接)

(select username,month,sum(count) as salary from t_access_times group by username,month) A 
join 
(select username,month,sum(count) as salary from t_access_times group by username,month) B
on 
A.username=B.username

+-------------+----------+-----------+-------------+----------+-----------+--+  
| a.username  | a.month  | a.salary  | b.username  | b.month  | b.salary  |  
+-------------+----------+-----------+-------------+----------+-----------+--+  
| A           | 2015-01  | 33        | A           | 2015-01  | 33        |  
| A           | 2015-01  | 33        | A           | 2015-02  | 10        |  
| A           | 2015-02  | 10        | A           | 2015-01  | 33        |  
| A           | 2015-02  | 10        | A           | 2015-02  | 10        |  
| B           | 2015-01  | 30        | B           | 2015-01  | 30        |  
| B           | 2015-01  | 30        | B           | 2015-02  | 15        |  
| B           | 2015-02  | 15        | B           | 2015-01  | 30        |  
| B           | 2015-02  | 15        | B           | 2015-02  | 15        |  
+-------------+----------+-----------+-------------+----------+-----------+--+  

3）第三步，从上一步的结果中进行分组查询，分组的字段是a.username a.month，求月累计值： 将b.month <= a.month的所有b.salary求和即可

3.HQL

SELECT
	A.username,
	A.month,
	MAX(A.count),
	SUM(B.count)
FROM
	(
		SELECT
			username,
			MONTH,
			SUM(COUNT) AS COUNT
		FROM
			t_accessgroup BY username,
			MONTH
	)
	A
INNER JOIN
	(
		SELECT
			username,
			MONTH,
			SUM(COUNT) AS COUNT
		FROM
			t_access
		GROUP BY
			username,
			MONTH
	)
	B
ON
	A.username = B.username
WHERE
	B.month <= A.month
GROUP BY
	A.username,
	A.month
ORDER BY
	A.username,
	A.month;

• Hive解析Json数据

HIVE直接读入json的函数有两个：

（1）get_json_object(string json_string, string path)

返回值: string

说明：解析json的字符串json_string,返回path指定的内容。如果输入的json字符串无效，那么返回NULL。

举例：

hive >
SELECT
	get_json_object(‘{“store”:{“fruit”:[{"weight":8, "type":"  apple"}, {"weight":9, "type":"  pear"}], “bicycle”:{“price”:19.95, ”color”:”red”}}, “email”:”amy@only_for_json_udf_test.net”, “owner”:”amy” } ‘, ’$.owner’)
FROM
	dual;

结果：amy

这个函数每次只能返回一个数据项。

（2）json_tuple(jsonStr, k1, k2, ...)

参数为一组键k1，k2……和JSON字符串，返回值的元组。该方法比 get_json_object 高效，因为可以在一次调用中输入多个键

SELECT
	a.timestamp,
	b.*
FROM
	log a lateral VIEW json_tuple(a.appevent, 'eventid', 'eventname') b AS f1,
	f2;

处理数据样例：

{"GPS_LAT":39.8965125, "GPS_LONG":116.3493225, "GPS_SPEED":20.9993625, "GPS_STATE":" A", "GPS_TIME":" 2014-01-02 00:00:16", "IMEI":" 508597", "after_oxygen_sensor":132, "air_condion_state":3, "bdoneNo_after_mileage":0, "bdoneNo_zero_mileage":8044, "db_speed":22, "direction_angle":358.2585, "front_oxygen_sensor":64, "instant_fuel":233, "speed":1210, "torque":33, "total_fuel":0}

处理HIVE语句：

CREATE TABLE 2014jrtest AS
SELECT
	json_tuple(line, 'GPS_LAT', 'GPS_LONG', 'GPS_SPEED', 'GPS_STATE', 'GPS_TIME', 'IMEI', 'after_oxygen_sensor', 'air_condion_state', 'bdoneNo_after_mileage', 'bdoneNo_zero_mileage', 'db_speed', 'direction_angle', 'front_oxygen_sensor', 'instant_fuel', 'speed', 'torque', 'total_fuel')
FROM
	2014test;

hive之Json解析(普通Json和Json数组) 

• 1、查找员工编号emp_no为10001其自入职以来的薪水salary涨幅值growth

SELECT
	MAX(salary) - MIN(salary) AS growth
FROM
	salaries
GROUP BY
	emp_no
HAVING
	emp_no = '10001' 【严谨的思路】
SELECT
	(
	(
		SELECT
			salary
		FROM
			salaries
		WHERE
			emp_no = 10001
		ORDER BY
			to_date DESC LIMIT 1
	)
	-
	(
		SELECT salary FROM salaries WHERE emp_no = 10001 ORDER BY to_date ASC LIMIT 1
	)
	) AS growth

2、【累计求和】所有聚合函数都能用做窗口函数，其语法和专用窗口函数完全相同——sum(<汇总列>) over(<排序列>) as 别名；

SELECT
	emp_no,
	salary,
	SUM(salary) over(order by emp_no) AS running_total
FROM
	salaries
WHERE
	to_date = '9999-01-01';

【把所有小于等于当前编号的表s1和当前编号表s2联立起来，然后按照当前编号分组，计算出所有小于等于当前标号的工资总数】
SELECT
	b.emp_no,
	b.salary,
	SUM(a.salary) AS running_total
FROM
	salaries a
INNER JOIN salaries b
ON
	a.emp_no <= b.emp_no
	AND a.to_date = "9999-01-01"
	AND b.to_date = "9999-01-01"
GROUP BY
	b.emp_no,
	b.salary

3、对于employees表中，给出奇数行的first_name

select e1.first_name from employees as e1
    where (select count(e2.first_name) from employees as e2
               where e1.first_name >= e2.first_name)%2 = 1;

4、 EXISTS用于检查子查询是否至少会返回一行数据，该子查询实际上并不返回任何数据，而是返回值True或False
SQL中EXISTS的用法

select * from employees
where not exists  (select * from dept_emp where emp_no=employees.emp_no)

5、LIMIT 1 OFFSET 2 -- 去掉OFFSET排名倒数第一第二的时间，取倒数第三

【limit y,x和limit x offset y等价】
【LIMIT 后的数字代表返回几条记录，OFFSET 后的数字代表从第几条记录开始返回（第一条记录序号为0），也可理解为跳过多少条记录后开始返回】
【在 LIMIT X,Y 中，Y代表返回几条记录，X代表从第几条记录开始返回（第一条记录序号为0），切勿记反】

`以下的两种方式均表示取``2``,``3``,``4``三条条数据。`
`1``.select* from test LIMIT` `1``,``3``;`
`当limit后面跟两个参数的时候，第一个数表示要跳过的数量，后一位表示要取的数量。`
`2``.select * from test LIMIT` `3` `OFFSET` `1``;(在mysql` `5``以后支持这种写法)`
`当 limit和offset组合使用的时候，limit后面只能有一个参数，表示要取的的数量,offset表示要跳过的数量 。`

6、查找排除当前最大、最小salary之后的员工的平均工资avg_salary

select avg(salary) as avg_salary 
from salaries
where to_date = '9999-01-01' 
and salary<(select max(salary) from salaries) 
and salary>(select min(salary) from salaries)

7、统计gmv分布

SELECT
	percentile_approx(CAST(batch_gmv_amount AS DOUBLE), 0.95, 9999) AS q095,
	percentile_approx(CAST(batch_gmv_amount AS DOUBLE), 0.94, 9999) AS q094,
	percentile_approx(CAST(batch_gmv_amount AS DOUBLE), 0.93, 9999) AS q093,
	percentile_approx(CAST(batch_gmv_amount AS DOUBLE), 0.92, 9999) AS q092,
	percentile_approx(CAST(batch_gmv_amount AS DOUBLE), 0.91, 9999) AS q091,
	percentile_approx(CAST(batch_gmv_amount AS DOUBLE), 0.90, 9999) AS q090,
	percentile_approx(CAST(batch_gmv_amount AS DOUBLE), 0.85, 9999) AS q085,
	percentile_approx(CAST(batch_gmv_amount AS DOUBLE), 0.80, 9999) AS q080
FROM
	(
		SELECT
			id,
			batch_gmv_amount
		FROM
			mytable
	)
	c

 

 

 

 

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参考：

【SQL刷题】SQL语法学习与面试题练习