HIVE函数（二）

1、查看内置（预定义）函数

show  functions；

2、查看函数如何使用

hive> desc function upper;

upper(str) - Returns str with all characters changed to uppercase

Time taken: 0.063 seconds, Fetched: 1 row(s)

更详细：

hive> desc function extended upper;

upper(str) - Returns str with all characters changed to uppercase

Synonyms: ucase

Example:

  > SELECT upper('Facebook') FROM src LIMIT 1;

  'FACEBOOK'

Time taken: 0.009 seconds, Fetched: 5 row(s)

3、测试时间函数

hive> create table dual(x string);

hive> insert into table dual values('');

hive> select unix_timestamp() from dual; ===》时间戳

1528468146

hive> select current_date from dual;====》返回当前天

OK

2018-06-08

hive> select current_timestamp from dual;===》返回当前时间戳

OK

2018-06-08 22:31:53.817

hive> select year("2018-08-08 20:08:08") from dual;===》取年

OK

2018

hive> select cast(current_timestamp as date) from dual;===》用cast 将当前时间戳转化成date

OK

2018-06-08

4、测试字符函数

hive> select concat_ws(".","192","168","199","151") from dual;        ===》用.将后面字符连起来

OK

192.168.199.151

hive> select length ("123456789") from dual;            ===》取长度

OK

9

hive> select split("192.168.137.130","\\.") from dual;            ===》拆分

OK

["192","168","137","130"]

5、HIVE实现word count

hive> create table hive_wc(sentence string);            创建表

hive> load data local inpath '/home/hadoop/data/hive-wc.txt' into table hive_wc;        导入数据

hive> select * from hive_wc    ;

hello,world,welcome

hello,welcom

先用split函数将拆分成每隔单词

hive> select split(sentence,",") from hive_wc;

["hello","world","welcome"]

["hello","welcom"]

使用explode函数把每个单词放一行

hive> select explode(split(sentence,",")) from hive_wc;

hello

world

welcome

hello

welcom

最后使用group by 完成word count

hive> select word, count(1) as c   from (select explode(split(sentence,",")) as word from hive_wc) t     group by word ;

hello 2

welcom  1

welcome 1

world  1

6、josn_tuple 函数

hive> create table rating_json(json string);                ===》创建表

hive> load data local inpath '/home/hadoop/data/rating.json' into table rating_json;            ===》导入数据

hive> select * from rating_json limit 2;                                ===》查看数据

{"movie":"1193","rate":"5","time":"978300760","userid":"1"}

{"movie":"661","rate":"3","time":"978302109","userid":"1"}

hive> select   json_tuple(json,"movie","rate","time","userid") as (movie,rate,time,userid)   from rating_json limit 2;   》使用json_tuple函数取字段值

1193    5      978300760      1

661    3      978302109      1