Nested json data not captured by JSON_TABLE in oracle sql - sql

Question

I'm using Oracle 12c(12.2) to read json data in a table.
SELECT jt.name,
jt.employee_id,
jt.company
FROM JSON_TABLE ( BFILENAME ('DB_DIR', 'vv.json')
i've nested data in json output. The key:value in nested data start with a value
"past_work": "N.A" for a record.
for other many records below it, have actual values like
"past_work": [{ "company": "XXXXX", "title": "XXXX"}]
but because first record done have value and start and end brackets [], oracle not capturing below records nested values.
any idea how to capture below records?
Example: Actual data like below
SELECT
jt.company,
jt.title
FROM
JSON_TABLE(
'{
"employee_data": [
{ "employee_id": "111",
"past_work": "N/A"
},
{ "employee_id": "222",
"past_work": [
{"company": "XXXXX", "title": "XXXX"},
{"company": "YYYYY", "title": "YYYY"}
]
},
{ "employee_id": "333",
"past_work": [
{"company": "XXXXX", "title": "XXXX"},
{"company": "YYYYY", "title": "YYYY"}
]
}
]
}',
'$.past_work[*]'
COLUMNS (
company VARCHAR2(100) PATH '$.company',
title VARCHAR2(100) PATH '$.title'
)
)
AS jt
now when i execute above statment, i'm getting null for company values for emplyee_id 333 and below.
Thanks

Answer 1

If past_work is supposed to be an array of past (company, title) pairs, then the proper way to encode "no history" is not to use a string value like "N/A", but instead you should use an empty array, as I show in the code below. If you do it your way, you can still extract the data, but it will be exceptionally messy. If you use JSON, use it correctly.
Also, you said you want to extract company and title. Just those? That makes no sense. Rather, you probably want to extract the employee id for each employee, along with the work history. In the work history, I add a column "for ordinality" (to show which company was first, which was second, etc.) If you don't need it, just leave it out.
To access nested columns, you must use the nested clause in the columns specification.
select employee_id, ord, company, title
from json_table(
'{
"employee_data": [
{ "employee_id": "111",
"past_work": [ ]
},
{ "employee_id": "222",
"past_work": [
{"company": "XXXXX", "title": "XXXX"},
{"company": "YYYYY", "title": "YYYY"}
]
},
{ "employee_id": "333",
"past_work": [
{"company": "XXXXX", "title": "XXXX"},
{"company": "YYYYY", "title": "YYYY"}
]
}
]
}', '$.employee_data[*]'
columns (
employee_id varchar2(10) path '$.employee_id',
nested path '$.past_work[*]'
columns (
ord for ordinality,
company varchar2(10) path '$.company',
title varchar2(10) path '$.title'
)
)
) jt
order by employee_id, ord;
Output:
EMPLOYEE_ID ORD COMPANY TITLE
----------- --- ------- -----
111
222 1 XXXXX XXXX
222 2 YYYYY YYYY
333 1 XXXXX XXXX
333 2 YYYYY YYYY

Answer 2

First, the json snippet is malformed, it MUST be surrounded by {} in order to be parsable as a json object...
{"past_work": [{ "company": "XXXXX", "title": "XXXX"}]}
Then, you can tell the json parser that you want to pull the rows from the past_work element...
JSON_TABLE(<yourJsonString>, '$.past_work[*]')
The [*] tells the parser that past_work is an array, and to process that array in to rows of json objects, rather than just return the whole array as a single json object.
That gives something like...
SELECT
jt.company,
jt.title
FROM
JSON_TABLE(
'{
"past_work": [
{"company": "XXXXX", "title": "XXXX"},
{"company": "YYYYY", "title": "YYYY"}
]
}',
'$.past_work[*]'
COLUMNS (
company VARCHAR2(100) PATH '$.company',
title VARCHAR2(100) PATH '$.title'
)
)
AS jt
db<>fiddle demo
For more details, I recommend reading the docs:
https://docs.oracle.com/database/121/SQLRF/functions092.htm#SQLRF56973
EDIT: Updated example, almost a copy and paste from the docs
Please Read The Docs!
SELECT
jt.*
FROM
JSON_TABLE(
'{
"XX_data":[
{
"employee_id": "E1",
"full_name": "E1 Admin",
"past_work": "N/A"
},
{
"employee_id": "E2",
"full_name": "E2 Admin",
"past_work": [
{"company": "E2 PW1 C", "title": "E2 PW1 T"},
{"company": "E2 PW2 C", "title": "E2 PW2 T"},
]
},
]
}',
'$.XX_data[*]'
COLUMNS (
employee_id VARCHAR2(100) PATH '$.employee_id',
full_name VARCHAR2(100) PATH '$.full_name',
past_work VARCHAR2(100) PATH '$.past_work',
NESTED PATH '$.past_work[*]'
COLUMNS (
past_work_company VARCHAR2(100) PATH '$.company',
past_work_title VARCHAR2(100) PATH '$.title'
)
)
)
AS jt
Another db<>fiddle demo

Answer 3

Thanks all for the Comments. Have asked product team to provide data in correct format.