How do you index an array inside a JSON with an Oracle 12c query?

Question

I have a table "move" with one column "move_doc" which is a CLOB. The json stored inside has the structure:

{
moveid : "123",
movedate : "xyz",
submoves: [
{
submoveid: "1",
...
 },
{
submoveid : "2",
...
}
]
}

I know I can run an Oracle 12c query to access the submoves list with:

select move.move_doc.submoves from move move

How do I access particular submoves of the array? And the attributes inside a particular submove?

Answer 1

You have to use Oracle functions json_query and/or json_value like this:

SELECT json_value(move_doc, '$.submoves[0].submoveid' RETURNING NUMBER) FROM move;

returns 1 .

SELECT json_query(move_doc, '$.submoves[1]') FROM move;

would return the second JSON element, ie something like

{
submoveid : "2",
...
}

json_value is used to retrieve a scalar value, json_query is used to retrieve JSON values. You might also want to have a look at json_table which returns an SQL result table and thus can be used in Joins.

See this Oracle Doc for more examples

Answer 2

Beda here from the Oracle JSON team.

We have added a new multi-value index in release 21c allowing you to index values from a JSON array. Obviously, 21c is brand new and you want to know how to do this in older releases: Functional indexes (using JSON_Value function) are limited to a single value per JSON document and therefore are not capable to index array values. But: there is a 'JSON search index' which indexes your entire JSON document and therefore also values in the array. Another solution is to use a materialized view usign JSON_Table. This will expand the array values into separate rows.Then you can add a regular B-Tree index on that column.

Sample code here: JSON indexing with functional indexes and JSON search index https://livesql.oracle.com/apex/livesql/file/content_HN507PELCEEJGVNW4Q61L34DS.html

JSON and materialized views https://livesql.oracle.com/apex/livesql/file/content_HYMB1YBP4CPMG6T6MXY5G9X5L.html

Answer 3

From what I've looked, In Oracle, you can index the "whole array" as a single index entry, but not individual elements of an array.

NoSQL databases like MongoDB, Couchbase, Cassandra have "array/collection" indexes which can index individual elements or fields of objects within an array and query them.