Sql: Unpivot with dynamic column list - sql

Question

I am looking to do some unpivoting in sql, converting key-values into a list of IDs. The Column from the table is dynamic and will change weekly (mayhaps even daily).
Where there maybe more KEY Columns and values possibilities.
DATABASE.PUBLIC.IMPORT_TABLE
+-----------+--------+--------+--------+
| SOURCE_ID | KEY1 | KEY2 | [KEY3] |
+-----------+--------+--------+--------+
| 0001 | TRUE | FALSE | [TBD] |
| 0002 | TRUE | FALSE | [TBD] |
| 0003 | TRUE | TRUE | [TBD] |
| 0004 | TRUE | TRUE | [TBD] |
| 0005 | FALSE | TRUE | [TBD] |
+-----------+--------+--------+--------+
To manage the possible combinations there is a table which manages the key-value pairs, and gives them an ID. This table is used to manage the Columns I am interested in. Where sometimes if there there are additional Columns added and not in this table it will be excluded.
DATABASE.PUBLIC.KEY_VALUE_TABLE
+-----------+--------+--------+
| KEY | VALUE | KV_ID |
+-----------+--------+--------+
| KEY1 | TRUE | AAA |
| KEY1 | FALSE | BBB |
| KEY2 | TRUE | CCC |
| KEY2 | FALSE | DDD |
| [KEY3] | [TRUE] | [EEE] |
+-----------+--------+--------+
Using the following query. I am able to achieve the unpivot I am looking for. However it does not take into account changes in dynamic changes for KEY_VALUE_TABLE
CREATE OR REPLACE TABLE DATABASE.PUBLIC.FINAL_TABLE AS
SELECT SOURCE_ID
,LISTAGG(DISTINCT b.KV_ID, ',') within group (order by b.KV_ID desc) AS KV_ID
FROM (
SELECT DISTINCT SOURCE_ID, KEY, VALUE from DATABASE.PUBLIC.IMPORT_TABLE
UNPIVOT(VALUE for KEY in (KEY1,KEY2))
) a
LEFT JOIN DATABASE.PUBLIC.KEY_VALUE_TABLE b
ON (a.KEY=b.KEY AND a.VALUE=b.VALUE)
GROUP BY 1,2
Where the results look like the following
DATABASE.PUBLIC.FINAL_TABLE
+-----------+--------+--------+
| SOURCE_ID | KV_ID |
+-----------+--------+--------+
| 0001 | AAA,DDD |
| 0002 | AAA,DDD |
| 0003 | AAA,CCC |
| 0004 | AAA,CCC |
| 0005 | BBB,CCC |
+-----------+--------+--------+
Is there a way to have the UNPIVOT(VALUE for KEY in (KEY1,KEY2))
to something like UNPIVOT(VALUE for KEY in (SELECT DISTINCT KEY FROM KEY_VALUE_TABLE)). Note I already tried the latter and it does not work.
SQL has an issue using SELECT within the UNPIVOT
I have also tried using UNPIVOT(VALUE for KEY in ($KEY_LIST))
Where my variable is SET KEY_LIST = '[KEY1,KEY2]'
=> SET KEY_LIST = (SELECT listagg(KEY, ',') as my_strings FROM DATABASE.PUBLIC.KEY_VALUE_TABLE)
SQL has a limit on the size of variables.
Any Advice would be appreciated.
My next step is to create a Stored Procedure or a Function. Which takes in external variables. via javascript or something similar.