Hive: parsing JSON - json

Question

I am trying to get some values out of nested JSON for millions of rows (5 TB+ table). What is the most efficient way to do this?
Here is an example:
{"country":"US","page":227,"data":{"ad":{"impressions":{"s":10,"o":10}}}}
I need these values out of the above JSON:
Country Page impressions_s impressions_o
--------- ----- ------------- --------------
US 2 10 10
This is Hive's json_tuple function, I am not sure if this is the best function.
https://cwiki.apache.org/confluence/display/Hive/LanguageManual+UDF#LanguageManualUDF-getjsonobject

Answer 1

You can use get_json_object:
select get_json_object(fieldname, '$.country'),
get_json_object(fieldname, '$.data.ad.s') from ...
You will get better performance with json_tuple but I found a "how to" to get the values in json inside json;
To formating your table you can use something like this:
from table t lateral view
explode( split(regexp_replace(get_json_object(ln, ''$.data.ad.s'), '\\[|\\]', ''), ',' ) ) tb1 as s
this code above will transform you "Array" in a column.
form more: https://cwiki.apache.org/confluence/display/Hive/LanguageManual+UDF
I hope this help ...

Answer 2

Here is what you can quickly try , I would suggest to use Json-Ser-De.
nano /tmp/hive-parsing-json.json
{"country":"US","page":227,"data":{"ad":{"impressions":{"s":10,"o":10}}}}
Create base table :
hive > CREATE TABLE hive_parsing_json_table ( json string );
Load json file to Table :
hive > LOAD DATA LOCAL INPATH '/tmp/hive-parsing-json.json' INTO TABLE hive_parsing_json_table;
Query the table :
hive > select v1.Country, v1.Page, v4.impressions_s, v4.impressions_o
from hive_parsing_json_table hpjp
LATERAL VIEW json_tuple(hpjp.json, 'country', 'page', 'data') v1
as Country, Page, data
LATERAL VIEW json_tuple(v1.data, 'ad') v2
as Ad
LATERAL VIEW json_tuple(v2.Ad, 'impressions') v3
as Impressions
LATERAL VIEW json_tuple(v3.Impressions, 's' , 'o') v4
as impressions_s,impressions_o;
Output :
v1.country v1.page v4.impressions_s v4.impressions_o
US 227 10 10

Answer 3

Using hive native json-serde('org.apache.hive.hcatalog.data.JsonSerDe') you can do this.. here are the steps
ADD JAR /path/to/hive-hcatalog-core.jar;
create a table as below
CREATE TABLE json_serde_nestedjson (
country string,
page int,
data struct < ad: struct < impressions: struct < s:int, o:int > > >
)
ROW FORMAT SERDE 'org.apache.hive.hcatalog.data.JsonSerDe';
then load data(stored in file)
LOAD DATA LOCAL INPATH '/tmp/nested.json' INTO TABLE json_serde_nestedjson;
then get required data using
SELECT country, page, data.ad.impressions.s, data.ad.impressions.o
FROM json_serde_nestedjson;

Answer 4

Implementing a SerDe to parse your data in JSON is a better way for your case.
A tutorial on how to implement SerDe for parsing JSON can be found here
http://blog.cloudera.com/blog/2012/12/how-to-use-a-serde-in-apache-hive/
You can use the following sample SerDe implementation as well
https://github.com/rcongiu/Hive-JSON-Serde