Query json dictionary data in SQL - sql

Question

My CLOB field in a table contains JSON and looks as following:
{"a":"value1", "b":"value2", "c":"value3"}
And I'm trying to write an SQL query to return a table with key and value fields like following:
key|value
---|------
a |value1
b |value2
c |value3
Any help would be hugely appreciated!

Answer 1

Use JSON_TABLE and then UNPIVOT if you want the values in rows instead of columns:
SELECT *
FROM (
SELECT p.*
FROM table_name t
CROSS JOIN
JSON_TABLE(
t.value,
'$'
COLUMNS (
a PATH '$.a',
b PATH '$.b',
c PATH '$.c'
)
) p
)
UNPIVOT ( value FOR key IN ( a, b, c ) );
So for some sample data:
CREATE TABLE table_name (
value CLOB CONSTRAINT ensure_json CHECK (value IS JSON)
);
INSERT INTO table_name ( value ) VALUES ( '{"a":"value1", "b":"value2", "c":"value3"}' );
This outputs:
KEY | VALUE
:-- | :-----
A | value1
B | value2
C | value3
db<>fiddle here
If you want to do it dynamically then you can parse the JSON in PL/SQL and use GET_KEYS to get a collection of key names and then access the correct one by its position and correlate that to the value using FOR ORDINALITY:
CREATE FUNCTION get_key(
pos IN PLS_INTEGER,
json IN CLOB
) RETURN VARCHAR2
AS
doc_keys JSON_KEY_LIST;
BEGIN
doc_keys := JSON_OBJECT_T.PARSE ( json ).GET_KEYS;
RETURN doc_keys( pos );
END get_key;
/
Then:
SELECT get_key( j.pos, t.value ) AS key,
j.value
FROM table_name t
CROSS APPLY JSON_TABLE(
t.value,
'$.*'
COLUMNS (
pos FOR ORDINALITY,
value PATH '$'
)
) j;
Outputs:
KEY | VALUE
:-- | :-----
a | value1
b | value2
c | value3
db<>fiddle here