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除了使用础的数据类型string等,Hive中的列支持使用struct, map, array集合数据类型。
数据类型 | 描述 | 语法示例 |
---|---|---|
STRUCT | 和C语言中的struct或者"对象"类似,都可以通过"点"符号访问元素内容。 | struct{'John', 'Doe'} |
MAP | MAP是一组键-值对元素集合,使用key可以访问元素。 | map('fisrt', 'John', 'last', 'Doe') |
ARRAY | 数组是一组具有相同数据类型和名称的变量的集合。 | Array('John', 'Doe') |
1. Array的使用
创建数据库表,以array作为数据类型
- create table person(name string,work_locations array
) - ROW FORMAT DELIMITED
- FIELDS TERMINATED BY '\t'
- COLLECTION ITEMS TERMINATED BY ',';
数据
- biansutao beijing,shanghai,tianjin,hangzhou
- linan changchu,chengdu,wuhan
入库数据
- LOAD DATA LOCAL INPATH '/home/hadoop/person.txt' OVERWRITE INTO TABLE person;
查询
- hive> select * from person;
- biansutao ["beijing","shanghai","tianjin","hangzhou"]
- linan ["changchu","chengdu","wuhan"]
- Time taken: 0.355 seconds
- hive> select name from person;
- linan
- biansutao
- Time taken: 12.397 seconds
- hive> select work_locations[0] from person;
- changchu
- beijing
- Time taken: 13.214 seconds
- hive> select work_locations from person;
- ["changchu","chengdu","wuhan"]
- ["beijing","shanghai","tianjin","hangzhou"]
- Time taken: 13.755 seconds
- hive> select work_locations[3] from person;
- NULL
- hangzhou
- Time taken: 12.722 seconds
- hive> select work_locations[4] from person;
- NULL
- NULL
- Time taken: 15.958 seconds
2. Map 的使用
创建数据库表
- create table score(name string, score map
int>) - ROW FORMAT DELIMITED
- FIELDS TERMINATED BY '\t'
- COLLECTION ITEMS TERMINATED BY ','
- MAP KEYS TERMINATED BY ':';
要入库的数据
- biansutao '数学':80,'语文':89,'英语':95
- jobs '语文':60,'数学':80,'英语':99
入库数据
- LOAD DATA LOCAL INPATH '/home/hadoop/score.txt' OVERWRITE INTO TABLE score;
查询
- hive> select * from score;
- biansutao {"数学":80,"语文":89,"英语":95}
- jobs {"语文":60,"数学":80,"英语":99}
- Time taken: 0.665 seconds
- hive> select name from score;
- jobs
- biansutao
- Time taken: 19.778 seconds
- hive> select t.score from score t;
- {"语文":60,"数学":80,"英语":99}
- {"数学":80,"语文":89,"英语":95}
- Time taken: 19.353 seconds
- hive> select t.score['语文'] from score t;
- 60
- 89
- Time taken: 13.054 seconds
- hive> select t.score['英语'] from score t;
- 99
- 95
- Time taken: 13.769 seconds
修改map字段的分隔符
- Storage Desc Params:
- colelction.delim ##
- field.delim \t
- mapkey.delim =
- serialization.format \t
可以通过desc formatted tableName查看表的属性。
hive-2.1.1中,可以看出colelction.delim,这里是colelction而不是collection,hive里面这个单词写错了,所以还是要按照错误的来。
- alter table t8 set serdepropertyes('colelction.delim'=',');
3. Struct 的使用
创建数据表
- CREATE TABLE test(id int,course struct
int>) - ROW FORMAT DELIMITED
- FIELDS TERMINATED BY '\t'
- COLLECTION ITEMS TERMINATED BY ',';
数据
- 1 english,80
- 2 math,89
- 3 chinese,95
入库
- LOAD DATA LOCAL INPATH '/home/hadoop/test.txt' OVERWRITE INTO TABLE test;
查询
- hive> select * from test;
- OK
- 1 {"course":"english","score":80}
- 2 {"course":"math","score":89}
- 3 {"course":"chinese","score":95}
- Time taken: 0.275 seconds
- hive> select course from test;
- {"course":"english","score":80}
- {"course":"math","score":89}
- {"course":"chinese","score":95}
- Time taken: 44.968 seconds
- select t.course.course from test t;
- english
- math
- chinese
- Time taken: 15.827 seconds
- hive> select t.course.score from test t;
- 80
- 89
- 95
- Time taken: 13.235 seconds
4. 不支持组合的复杂数据类型
我们有时候可能想建一个复杂的数据集合类型,比如下面的a字段,本身是一个Map,它的key是string类型的,value是Array集合类型的。
建表
- create table test1(id int,a MAP
>) - row format delimited fields terminated by '\t'
- collection items terminated by ','
- MAP KEYS TERMINATED BY ':';
导入数据
- 1 english:80,90,70
- 2 math:89,78,86
- 3 chinese:99,100,82
-
- LOAD DATA LOCAL INPATH '/home/hadoop/test1.txt' OVERWRITE INTO TABLE test1;
这里查询出数据:
- hive> select * from test1;
- OK
- 1 {"english":["80"],"90":null,"70":null}
- 2 {"math":["89"],"78":null,"86":null}
- 3 {"chinese":["99"],"100":null,"82":null}
可以看到,已经出问题了,我们意图是想"english":["80", "90", "70"],实际上把90和70也当作Map的key了,value值都是空的。分析一下我们的建表语句,collection items terminated by ','制定了集合类型(map, struct, array)数据元素之间分隔符是", ",实际上map也是属于集合的,那么也会按照逗号分出3个key-value对;由于MAP KEYS TERMINATED BY ':'定义了map中key-value的分隔符是":",第一个“english”可以准确识别,后面的直接把value置为"null"了。