Preparation

Let’s create our table

CREATE TABLE tbl_json_example (
     id NUMBER PRIMARY KEY,
     st_character CLOB,
     st_ship CLOB
);

and add some data to it

INSERT INTO tbl_json_example (id, st_character, st_ship) VALUES (
   1, 
   '{"character": "Captain Jean-Luc Picard", "rank": "Captain"}', 
   '{"ship": "USS Enterprise-D", "registry": "NCC-1701-D", "class": "Galaxy-class", "species": "Human"}'
);
INSERT INTO tbl_json_example (id, st_character, st_ship) VALUES (
   2, 
   '{"character": "Commander Spock", "rank": "Commander"}', 
   '{"ship": "USS Enterprise", "registry": "NCC-1701", "class": "Constitution-class", "species": "Vulcan"}'
);
INSERT INTO tbl_json_example (id, st_character, st_ship) VALUES (
   3, 
   '{"character": "Captain Kathryn Janeway", "rank": "Captain"}', 
   '{"ship": "USS Voyager", "registry": "NCC-74656", "class": "Intrepid-class", "species": "Human"}'
);

Now le’ts have a look if everything is fine so far

Our goal is now to move the attribute „species“ from the ship column into the character column.

Solution with JSON_MERGEPATCH

Oracle 19c provides a function called JSON_MERGEPATCH to update specific portions of a JSON. So let’s have a closer look to see if this is what we’re looking for

SELECT json_mergepatch(st_character, '{"species": "SOME_VALUE"}') from tbl_json_example;

Looks fine so far

Now let’s extend the whole thing so the attribute „species“ is read from the ST_SHIP column and added to the ST_CHARACTER column and put it into an UPDATE statement

UPDATE tbl_json_example SET st_character = json_mergepatch(st_character, '{"species": "' || json_value(st_ship, '$.species') || '"}');

It works, nice!

Since we don’t want the attribute in our ST_SHIP column, let’s delete it. Again, first with a SELECT statement

SELECT json_mergepatch(st_ship, '{"species": null}') from tbl_json_example;

Good

Now for the DELETE statement

UPDATE tbl_json_example SET st_ship = json_mergepatch(st_ship, '{"species": null}');

Final result

Be careful, if your target colum already has JSON attributes, that you want to merge. The function will override them.

Alternative with JSON_TRANSFORM

Since JSON_MERGEPATCH is only available from Oracle 19c on, there is an alternative for the 12c users (sorry if you use older versions)

For insertion

SELECT JSON_TRANSFORM(st_character, SET '$.species' = json_value(st_ship, '$.species')) from tbl_json_example;

and deletion

SELECT JSON_TRANSFORM(st_ship, REMOVE '$.species') from tbl_json_example;

Sources:

https://docs.oracle.com/en/database/oracle/oracle-database/21/adjsn/oracle-sql-function-json_transform.html#GUID-7BED994B-EAA3-4FF0-824D-C12ADAB862C1

https://docs.oracle.com/en/database/oracle/oracle-database/21/adjsn/oracle-sql-function-json_mergepatch.html#GUID-80B4DA1C-246F-4AB4-8DF5-D492E5661AA8

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