hive中array嵌套map以及行转列的使用

1. 数据源信息

{"student": {"name":"king","age":11,"sex":"M"},"sub_score":[{"subject":"语文","score":80},{"subject":"数学","score":80},{"subject":"英语","score":80}]}
{"student": {"name":"king1","age":11,"sex":"M"},"sub_score":[{"subject":"语文","score":81},{"subject":"数学","score":80},{"subject":"英语","score":80}]}
{"student": {"name":"king2","age":12,"sex":"M"},"sub_score":[{"subject":"语文","score":82},{"subject":"数学","score":80},{"subject":"英语","score":80}]}
{"student": {"name":"king3","age":13,"sex":"M"},"sub_score":[{"subject":"语文","score":83},{"subject":"数学","score":80},{"subject":"英语","score":80}]}
{"student": {"name":"king4","age":14,"sex":"M"},"sub_score":[{"subject":"语文","score":84},{"subject":"数学","score":80},{"subject":"英语","score":80}]}
{"student": {"name":"king5","age":15,"sex":"M"},"sub_score":[{"subject":"语文","score":85},{"subject":"数学","score":80},{"subject":"英语","score":80}]}
{"student": {"name":"king5","age":16,"sex":"M"},"sub_score":[{"subject":"语文","score":86},{"subject":"数学","score":80},{"subject":"英语","score":80}]}
{"student": {"name":"king5","age":17,"sex":"M"},"sub_score":[{"subject":"语文","score":87},{"subject":"数学","score":80},{"subject":"英语","score":80}]}

2. 创建hive表

分析数据源，由于是json格式，

student字段使用map结构，sub_score字段使用array嵌套map的格式，

这样使用的好处是如果数据源中只要第一层字段不会改变，都不会有任何影响，兼容性较强。

创建表语句如下, 注意使用下面这个json包，这样解析json出错时不至于程序挂掉。

下载地址：

https://github.com/rcongiu/Hive-JSON-Serde

http://www.congiu.net/hive-json-serde/

create external table if not exists dw_stg.stu_score(
student map<string,string> comment "学生信息",
sub_score array<map<string,string>> comment '成绩表'
)
comment "学生成绩表"
row format serde 'org.apache.hive.hcatalog.data.JsonSerDe' 
ROW FORMAT SERDE 'org.openx.data.jsonserde.JsonSerDe'
stored as textfile;

对于解析异常时报错的处理，可以加上一下属性：

ALTER TABLE dw_stg.stu_score SET SERDEPROPERTIES ( "ignore.malformed.json" = "true");

3. 上传数据

将score.txt数据上传到hive表stu_score目录：

hdfs dfs -put score.txt hdfs://dwtest-name1:9000/user/hive/warehouse/dw_stg.db/stu_score/

4. 数据查询

1）普通查询

2）查询单个学生的成绩

3）行转列explode ★★★

select explode(sub_score) from stu_score where student['name'] = 'king1';

4）更高级的写法：行转列lateral view .... explode ★★★

当使用explode时，不支持使用其他字段，如下会报错

所以使用另外一种用法

select student['name'],score['subject'],score['score']
from stu_score
lateral view explode(sub_score) sc as score
where student['name'] = 'king1';

5）保留null字段值 。格式 lateral view outer explode(field) 

如果数据源中学生分数为空时，在查询时可能就不会显示出来。比如下面的数据中，小明没有成绩。

使用4）中的查询显示如下：

此时，如果希望将小明也显示出来，则可以使用 lateral view outer explode(field) 格式。

select student['name'],score
from stu_score
lateral view outer explode(sub_score) sc as score 

或者下面

通过3）、4）、5）步骤基本可以实现所有字段的任意查询和使用了。