Oracle Left join with a list - oracle

Question

I am trying to use a list in my left join and it isn't working, but I'm also not getting an error. It's just not returning data.
Here's the data sample
Colors
| Color ID | Color |
| -------- | -------------- |
| 1 | Red |
| 2 | Blue |
| 3 | Green |
| 4 | Yellow |
Flags
| Flag | ColorList|
| -------- | ----- |
| country1 | 1 |
| country2 | 3 |
| country3 | 1,3 |
| country4 | 1,3,4 |
My Query
select f.flag, f.colorList, c.colorID, c.color
from flags f LEFT JOIN colors c ON to_char(c.colorID) IN f.colorList
The output I'm getting - any country that has a list instead of one value isn't returning anything
| Flag | List | colorID | Color|
| -------- | ----- | --- | --- |
| country1 | 1 |1 |red |
| country2 | 3 |3 |green |
| country3 | 1,3 |
| country4 | 1,3,4 |
The output I Want
| Flag | List | colorID | Color|
| -------- | ----- | --- | --- |
| country1 | 1 |1 |red |
| country2 | 3 |3 |green |
| country3 | 1,3 |1 |red |
| country3 | 1,3 |3 |green |
| country4 | 1,3,4 |1 |red |
| country4 | 1,3,4 |3 |green |
| country4 | 1,3,4 |4 |yellow|
I tried adding quotes and a couple other variations, but have not had success, but also no errors to help point me in the right direction. I've done a lot of searches to try to find the answers but haven't found anything straightforward.

Answer 1

You can use a CROSS JOIN to split your CSV list of colors so that you can get one row for each number in the list, then LEFT JOIN to your colors table
WITH
flags (flag, colorlist)
AS
(SELECT 'country1', '1' FROM DUAL
UNION ALL
SELECT 'country2', '3' FROM DUAL
UNION ALL
SELECT 'country3', '1,3' FROM DUAL
UNION ALL
SELECT 'country4', '1,3,4' FROM DUAL),
colors (color_id, color)
AS
(SELECT 1, 'Red' FROM DUAL
UNION ALL
SELECT 2, 'Blue' FROM DUAL
UNION ALL
SELECT 3, 'Green' FROM DUAL
UNION ALL
SELECT 4, 'Yellow' FROM DUAL)
--The Common Table Expressions are used to mock up the sample data. Actual query begins below
SELECT f.flag,
f.colorlist,
c.color_id,
c.color
FROM flags f
CROSS JOIN
TABLE (
CAST (
MULTISET ( SELECT REGEXP_SUBSTR (colorlist,
'[^,]+',
1,
LEVEL)
FROM DUAL
CONNECT BY LEVEL <= REGEXP_COUNT (colorlist, ',') + 1)
AS SYS.odciNumberList)) l
LEFT JOIN colors c ON (l.COLUMN_VALUE = c.color_id);