You can achieve that using LAG
function:
CREATE TABLE t_room_s (
room VARCHAR2(20),
address VARCHAR2(20)
);
INSERT INTO t_room_s VALUES ('room1', 'addr 1');
INSERT INTO t_room_s VALUES ('room2', 'addr 1');
INSERT INTO t_room_s VALUES ('room3', 'addr 2');
INSERT INTO t_room_s VALUES ('room4', 'addr 3');
INSERT INTO t_room_s VALUES ('room5', 'addr 4');
INSERT INTO t_room_s VALUES ('room6', 'addr 4');
INSERT INTO t_room_s VALUES ('room7', 'addr 4');
INSERT INTO t_room_s VALUES ('room8', 'addr 5');
SELECT wm_concat(room || ' ' || addr) AS val
FROM (
SELECT
room,
CASE
WHEN LAG(address, 1, NULL) OVER (ORDER BY address) = address THEN 'same address'
ELSE address
END AS addr
FROM
t_room_s
ORDER BY address
)
;
Output:
VAL ------------------------------------------------------------------------------------------------------------------------- room1 addr 1,room2 same address,room3 addr 2,room4 addr 3,room5 addr 4,room6 same address,room7 same address,room8 addr 5