Sets From a Single Table, Grouped By a Column - oracle

Question

I have a table:
+-------+-------+----------+
| GROUP | State | Priority |
+-------+-------+----------+
| 1 | MI | 1 |
| 1 | IA | 2 |
| 1 | CA | 3 |
| 1 | ND | 4 |
| 1 | AZ | 5 |
| 2 | IA | 2 |
| 2 | NJ | 1 |
| 2 | NH | 3 |
And so on...
How do I write a query that makes all the sets of the states by group, in priority order? Like so:
+-------+--------------------+
| GROUP | SET |
+-------+--------------------+
| 1 | MI |
| 1 | MI, IA |
| 1 | MI, IA, CA |
| 1 | MI, IA, CA, ND |
| 1 | MI, IA, CA, ND, AZ |
| 2 | NJ |
| 2 | NJ, IA |
| 2 | NJ, IA, NH |
+-------+--------------------+
This is similar to my question here and I've tried to modify that solution but, I'm just a forty watt bulb and it's a sixty watt problem...

Answer 1

This problem actually looks simpler than the answer to the question you linked, which is an excellent solution to that problem. Nevertheless, this uses the same hierarchical queries, with connect by
If it is the case that priority is always a continuous sequence of numbers, this will work
SELECT t.grp, level, ltrim(SYS_CONNECT_BY_PATH(state,','),',') as "set"
from t
start with priority = 1
connect by priority = prior priority + 1
and grp = prior grp
However, if that's not always true, we would require row_number() to define the sequence based on the order of priority ( which need not be consecutive integer)
with t2 AS
(
select t.*, row_number()
over ( partition by grp order by priority) as rn from t
)
SELECT t2.grp, ltrim(SYS_CONNECT_BY_PATH(state,','),',') as "set"
from t2
start with priority = 1
connect by rn = prior rn + 1
and grp = prior grp
DEMO

Answer 2

I realize this has already been answered, but I wanted to see if I could do this using ANSI standard syntax. "connect by" is an Oracle only feature, the following will work on multiple databases:
WITH
-- ASET is just setting up the sample dataset
aset AS
(SELECT 1 AS grp, 'MI' AS state, 1 AS priority FROM DUAL
UNION ALL
SELECT 1 AS grp, 'IA', 2 FROM DUAL
UNION ALL
SELECT 1 AS grp, 'CA', 3 FROM DUAL
UNION ALL
SELECT 1 AS grp, 'ND', 4 FROM DUAL
UNION ALL
SELECT 1 AS grp, 'AZ', 5 FROM DUAL
UNION ALL
SELECT 2 AS grp, 'IA', 2 FROM DUAL
UNION ALL
SELECT 2 AS grp, 'NJ', 1 FROM DUAL
UNION ALL
SELECT 2 AS grp, 'NH', 3 FROM DUAL),
bset AS
-- In BSET we convert the ASET records into comma separated values
( SELECT grp, LISTAGG( state, ',' ) WITHIN GROUP (ORDER BY priority) AS set1
FROM aset
GROUP BY grp),
cset ( grp
, set1
, set2
, pos ) AS
-- CSET breaks our comma separated values up into multiple rows
-- Each row adding the next CSV value
(SELECT grp AS grp
, set1 AS set1
, SUBSTR( set1 || ',', 1, INSTR( set1 || ',', ',' ) - 1 ) AS set2
, 1 AS pos
FROM bset
UNION ALL
SELECT grp AS grp
, set1 AS set1
, SUBSTR( set1 || ','
, 1
, INSTR( set1 || ','
, ','
, 1
, pos + 1 )
- 1 ) AS set2
, pos + 1 AS pos
FROM cset
WHERE INSTR( set1 || ','
, ','
, 1
, pos + 1 ) > 0)
SELECT grp, set2
FROM cset
ORDER BY grp, pos;