How to get array index from Oracle JSON column? - json

Question

Having a JSON like this (I know that JSON doesn't support comments. Used in this case to illustrate the idea):
{
"people": [
{ --// <-- index 0
"id": 100,
"name": "John Doe"
},
{ --// <-- index 1
"id": 101,
"name": "Jane Roe"
}
]
}
We can select values from specific elements in the array doing something like this:
SELECT name
FROM JSON_TABLE(
'{
"people": [
{
"id": 100,
"name": "John Doe"
},
{
"id": 101,
"name": "Jane Roe"
},
]
}', '$.people[*]'
COLUMNS(
ID NUMBER PATH '$.id',
NAME VARCHAR2 PATH '$.name'
)
) info
WHERE info.id = 101
Result:
NAME
--------
Jane Roe
Is there a way to get the element index in the array? Something like:
SELECT array_index --// <-- how get the array index of the element found?
FROM JSON_TABLE(
--// ...
) info
WHERE info.id = 101
Result:
ARRAY_INDEX
-----------
1
Is possible to do something like this using JSON support in Oracle 12c?

Answer 1

COLUMNS(
idx FOR ORDINALITY,
ID NUMBER PATH '$.id',
NAME VARCHAR2 PATH '$.name'
)
should work for you

Answer 2

As ArtBajji wrote, the rows itself dont have a index. Therefor you need to create a "fake id" that is relatively fixed.
This can be achieved by giving your data a order(order by id) and a index (rownum). Then select from this "modified" table
SELECT name, indx FROM (
SELECT ind.*, rownum "INDX"
FROM JSON_TABLE(
'{
"people": [
{
"id": 100,
"name": "John Doe"
},
{
"id": 101,
"name": "Jane Roe"
},
]
}', '$.people[*]'
COLUMNS(
ID NUMBER PATH '$.id',
NAME VARCHAR2 PATH '$.name'
)
) ind order by id) tab
WHERE tab.id = 101
Yields 1 for id 100 and 2 for id 101.
Be aware that the index of the elements 100 and 101 grow by one if you insert a item with a id < 100.