Ability to get the "index" (or ordinal value) for each array entry in BigQuery? - sql

Question

In a data column in BigQuery, I have a JSON object with the structure:
{
"sections": [
{
"secName": "Flintstones",
"fields": [
{ "fldName": "Fred", "age": 55 },
{ "fldName": "Barney", "age": 44 }
]
},
{
"secName": "Jetsons",
"fields": [
{ "fldName": "George", "age": 33 },
{ "fldName": "Elroy", "age": 22 }
]
}
]}
I'm hoping to unnest() and json_extract() to get results that resemble:
id | section_num | section_name | field_num | field_name | field_age
----+--------------+--------------+-----------+------------+-----------
1 | 1 | Flintstones | 1 | Fred | 55
1 | 1 | Flintstones | 2 | Barney | 44
1 | 2 | Jetsons | 1 | George | 33
1 | 2 | Jetsons | 2 | Elroy | 22
So far, I have the query:
SELECT id,
json_extract_scalar(curSection, '$.secName') as section_name,
json_extract_scalar(curField, '$.fldName') as field_name,
json_extract_scalar(curField, '$.age') as field_age
FROM `tick8s.test2` AS tbl
LEFT JOIN unnest(json_extract_array(tbl.data, '$.sections')) as curSection
LEFT JOIN unnest(json_extract_array(curSection, '$.fields')) as curField
that yields:
id | section_name | field_name | field_age
----+--------------+------------+-----------
1 | Flintstones | Fred | 55
1 | Flintstones | Barney | 44
1 | Jetsons | George | 33
1 | Jetsons | Elroy | 22
QUESTION: I'm not sure how, if possible, to get the section_num and field_num ordinal positions from their array index values?
(If you are looking to duplicate my results, I have a table named test2 with 2 columns:
id - INTEGER, REQUIRED
data - STRING, NULLABLE
and I insert the data with:
insert into tick8s.test2 values (1,
'{"sections": [' ||
'{' ||
'"secName": "Flintstones",' ||
'"fields": [' ||
'{ "fldName": "Fred", "age": 55 },' ||
'{ "fldName": "Barney", "age": 44 }' ||
']' ||
'},' ||
'{' ||
'"secName": "Jetsons",' ||
'"fields": [' ||
'{ "fldName": "George", "age": 33 },' ||
'{ "fldName": "Elroy", "age": 22 }' ||
']' ||
'}]}'
);
)

Answer 1

Do you just want with offset?
SELECT id,
json_extract_scalar(curSection, '$.secName') as section_name,
n_s,
json_extract_scalar(curField, '$.fldName') as field_name,
json_extract_scalar(curField, '$.age') as field_age,
n_c
FROM `tick8s.test2` tbl LEFT JOIN
unnest(json_extract_array(tbl.data, '$.sections')
) curSection WITH OFFSET n_s LEFT JOIN
unnest(json_extract_array(curSection, '$.fields')
) curField WITH OFFSET n_c;