本文转载自微信公众号「Java大数据与数据仓库」，作者柯同学。转载本文请联系Java大数据与数据仓库公众号。
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 ' ' 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/' OVERWRITE INTO TABLE person;
查询
hive> select * from person; biansutao ["beijing","shanghai","tianjin","hangzhou"] linan ["changchu","chengdu","wuhan"] Time taken: seconds hive> select name from person; linan biansutao Time taken: seconds hive> select work_locations[0] from person; changchu beijing Time taken: seconds hive> select work_locations from person; ["changchu","chengdu","wuhan"] ["beijing","shanghai","tianjin","hangzhou"] Time taken: seconds hive> select work_locations[3] from person; NULL hangzhou Time taken: seconds hive> select work_locations[4] from person; NULL NULL Time taken: seconds
2. Map 的使用
创建数据库表
create table score(name string, score map<string,int>) ROW FORMAT DELIMITED FIELDS TERMINATED BY ' ' 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/' 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: seconds hive> select name from score; jobs biansutao Time taken: seconds hive> select from score t; {"语文":60,"数学":80,"英语":99} {"数学":80,"语文":89,"英语":95} Time taken: seconds hive> select ['语文'] from score t; 60 89 Time taken: seconds hive> select ['英语'] from score t; 99 95 Time taken: seconds
修改map字段的分隔符
Storage Desc Params: ## =
可以通过desc formatted tableName查看表的属性。
hive-中，可以看出，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(''=',');
3. Struct 的使用
创建数据表
CREATE TABLE test(id int,course struct<course:string,score:int>) ROW FORMAT DELIMITED FIELDS TERMINATED BY ' ' COLLECTION ITEMS TERMINATED BY ',';
数据
1 english,80 2 math,89 3 chinese,95
入库
LOAD DATA LOCAL INPATH '/home/hadoop/' 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: seconds hive> select course from test; {"course":"english","score":80} {"course":"math","score":89} {"course":"chinese","score":95} Time taken: seconds select from test t; english math chinese Time taken: seconds hive> select from test t; 80 89 95 Time taken: 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<STRING,ARRAY>) row format delimited fields terminated by ' ' 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/' 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。
