Hive函数

内置运算符

Hive官方文档

内置函数

Hive官方文档

Hive内置函数

测试各种内置函数的快捷方法：

1、创建一个dual表

create table dual(id string);

2、load data local inpath 'home/hadoop/dual.dat' into table dual;   一个文件（一行，一个空格）到dual表 

3、select substr('angelababy',2,3) from dual;  

select substr('angelababy',0,3) from dual;==>和下一句返回的一模一样

select substr('angelababy',1,3) from dual;==>和上一句返回的一模一样

4、select concat('a'，'b')from dual;

自定义函数和Transform

当Hive提供的内置函数无法满足你的业务处理需要时，此时就可以考虑使用用户自定义函数（UDF：user-defined function）。

1、创建一个java工程，将apache-hive-1.2.2-bin.tar.gz解压缩后的安装路径，找到lib文件夹，将其中的jar包放到工程中

2、创建包名cn.itcast.bigdata.udf

3、创建一个自定义类ToLowerCase--将传入的字符串变为小写

package cn.itcast.bigdata.udf;

import java.util.HashMap;

import org.apache.hadoop.hive.ql.exec.UDF;

public class ToLowerCase extends UDF {
	public static HashMap provinceMap = new HashMap();
	static {
		provinceMap.put("136", "beijing");
		provinceMap.put("137", "shanghai");
		provinceMap.put("138", "shenzhen");
	}

	// 必须是public--重载此方法
	public String evaluate(String field) {
		String result = field.toLowerCase();
		return result;
	}
        //必须是public--重载此方法--两个方法同样的不会有影响
	public String evaluate(int phonenbr) {
		
		String pnb = String.valueOf(phonenbr);
		return provinceMap.get(pnb.substring(0, 3)) == null ? "huoxing":provinceMap.get(pnb.substring(0,3));

	}

}

4、打成jar包，上传至hive节点的服务器，并在服务器添加hive函数，将jar包对应起来

hive>add JAR /home/hadoop/udf.jar;
Hive>create temporary function 自定义函数名tolow as 'cn.itcast.bigdata.udf.ToProvince';

5、查看select * from t_p;

6、添加数据 insert into t_p values(13,'ANGELA');

7、查看select * from t_p;可以看到大写的数据

8、select id,自定义函数名tolow(name) from t_p;可以看到已变成小写，selct时，我们对name进行函数处理，导致小写

Hive>create temporary function 自定义函数名getprovince as 'cn.itcast.bigdata.udf.ToProvince';

select phonenbr,自定义函数名getprovince(phonenbr),flow from t_flow;

Hive自定义函数类别

UDF  作用于单个数据行，产生一个数据行作为输出。（数学函数，字符串函数）

UDAF（用户定义聚集函数）：接收多个输入数据行，并产生一个输出数据行。（count，max）

UDF开发实例

l  简单UDF示例

1、先开发一个java类，继承UDF，并重载evaluate方法

package cn.itcast.bigdata.udf
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.Text;
 
public final class Lower extends UDF{
     public Text evaluate(final Text s){
          if(s==null){return null;}
          return new Text(s.toString().toLowerCase());
     }
} 

2、打成jar包上传到服务器

3、将jar包添加到hive的classpath
hive> add JAR /home/hadoop/udf.jar;

4、创建临时函数与开发好的java class关联

Hive>create temporary function 自定义函数名 as 'cn.itcast.bigdata.udf.ToProvince';

5、即可在hql中使用自定义的函数strip 

select 自定义函数名(name),age from t_test;

l  Json数据解析UDF开发

数据准备

{"movie":"1193","rate":"5","timeStamp":"978300760","uid":"1"}
{"movie":"661","rate":"3","timeStamp":"978302109","uid":"1"}
{"movie":"914","rate":"3","timeStamp":"978301968","uid":"1"}
{"movie":"3408","rate":"4","timeStamp":"978300275","uid":"1"}
{"movie":"2355","rate":"5","timeStamp":"978824291","uid":"1"}
{"movie":"1197","rate":"3","timeStamp":"978302268","uid":"1"}
{"movie":"1287","rate":"5","timeStamp":"978302039","uid":"1"}
{"movie":"2804","rate":"5","timeStamp":"978300719","uid":"1"}
{"movie":"594","rate":"4","timeStamp":"978302268","uid":"1"}
{"movie":"919","rate":"4","timeStamp":"978301368","uid":"1"}
{"movie":"595","rate":"5","timeStamp":"978824268","uid":"1"}
{"movie":"938","rate":"4","timeStamp":"978301752","uid":"1"}
{"movie":"2398","rate":"4","timeStamp":"978302281","uid":"1"}
{"movie":"2918","rate":"4","timeStamp":"978302124","uid":"1"}
{"movie":"1035","rate":"5","timeStamp":"978301753","uid":"1"}
{"movie":"2791","rate":"4","timeStamp":"978302188","uid":"1"}
{"movie":"2687","rate":"3","timeStamp":"978824268","uid":"1"}
{"movie":"2018","rate":"4","timeStamp":"978301777","uid":"1"}
{"movie":"3105","rate":"5","timeStamp":"978301713","uid":"1"}
{"movie":"2797","rate":"4","timeStamp":"978302039","uid":"1"}

1、create table t_json(line string) row format delimited;

2、load data local inpath 'home/hadoop/rating.json' into table t_json;

3、select * from t_json limit 10;

4、自定义类JsonParser

package cn.itcast.bigdata.udf;
import org.apache.hadoop.hive.ql.exec.UDF;
import parquet.org.codehaus.jackson.map.ObjectMapper;//之前已经将lib的jar包添加到工程中

public class JsonParser extends UDF {

	public String evaluate(String jsonLine) {

		ObjectMapper objectMapper = new ObjectMapper();

		try {
			MovieRateBean bean = objectMapper.readValue(jsonLine, MovieRateBean.class);
			return bean.toString();
		} catch (Exception e) {

		}
		return "";
	}

}

MovieRateBean

package cn.itcast.bigdata.udf;

//{"movie":"1721","rate":"3","timeStamp":"965440048","uid":"5114"}属性名必须和key一模一样
public class MovieRateBean {
        
	private String movie;
	private String rate;
	private String timeStamp;
	private String uid;
        //碍于篇幅 --这里隐藏get和set方法
	@Override
	public String toString() {//解析后返回字符串
		return movie + "\t" + rate + "\t" + timeStamp + "\t" + uid;
	}


}

5、打包上传至服务器、将包添加至hive的classpath

6、Hive>create temporary function 自定义函数名parsejson as 'cn.itcast.bigdata.udf.Parsejson';

7、查看数据select parsejson(line) from t_json limit 10;

8、其他方式

create table rat_json(line string) row format delimited;
load data local inpath '/home/hadoop/rating.json' into table rat_json;

drop table if exists t_rating;
create table t_rating(movieid string,rate int,timestring string,uid string)
row format delimited fields terminated by '\t';

insert overwrite table t_rating 新创建表t_rating
select split得到数组(自定义函数parsejson(line),'\t')[0]as movieid,
split(parsejson(line),'\t')[1] as rate,
split(parsejson(line),'\t')[2] as timestring,
split(parsejson(line),'\t')[3] as uid 
from rat_json limit 10;

Transform实现

Hive的 TRANSFORM 关键字提供了在SQL中调用自写脚本的功能

适合实现Hive中没有的功能又不想写UDF的情况

使用示例1：下面这句sql就是借用了weekday_mapper.py对数据进行了处理.

CREATE TABLE u_data_new (
  movieid INT,
  rating INT,
  weekday INT,
  userid INT)
ROW FORMAT DELIMITED
FIELDS TERMINATED BY '\t';
 
add FILE weekday_mapper.py;//如果是java则是add jar
 
INSERT OVERWRITE TABLE u_data_new
SELECT
  TRANSFORM (movieid , rate, timestring,uid)//查询4个字段用python脚本来处理
  USING 'python weekday_mapper.py'
  AS (movieid, rating, weekday,userid) //将time string转化为星期几 as返回4个结果
FROM t_rating;

其中weekday_mapper.py内容如下

#!/bin/python
import sys
import datetime
 
for line in sys.stdin:
  line = line.strip()
  movieid, rating, unixtime,userid = line.split('\t')
  weekday = datetime.datetime.fromtimestamp(float(unixtime)).isoweekday()
  print '\t'.join([movieid, rating, str(weekday),userid])//左右字段加入/t分隔符

步骤整理：

transform案例:

1、先加载rating.json文件到hive的一个原始表 rat_json
create table rat_json(line string) row format delimited;
load data local inpath '/home/hadoop/rating.json' into table rat_json;

2、需要解析json数据成四个字段，插入一张新的表 t_rating
insert overwrite table t_rating
select get_json_object(line,'$.movie') as moive,get_json_object(line,'$.rate') as rate  from rat_json;

3、使用transform+python的方式去转换unixtime为weekday
先编辑一个python脚本文件
########python######代码
vi weekday_mapper.py
#!/bin/python
import sys
import datetime

for line in sys.stdin:
  line = line.strip()
  movieid, rating, unixtime,userid = line.split('\t')
  weekday = datetime.datetime.fromtimestamp(float(unixtime)).isoweekday()
  print '\t'.join([movieid, rating, str(weekday),userid])

保存文件
然后，将文件加入hive的classpath：
hive>add FILE /home/hadoop/weekday_mapper.py;
hive>create TABLE u_data_new as//通过查询得到数据
SELECT
  TRANSFORM (movieid, rate, timestring,uid)//和t_rating对应 作为输入传递到python脚本
  USING 'python weekday_mapper.py'
  AS (movieid, rate, weekday,uid)//根据结果 另外一个表的字段 插入到新表u_data_new
FROM t_rating;

select distinct(weekday) from u_data_new limit 10;