これを試して
SELECT ID,SUBSTRING_INDEX(SUBSTRING_INDEX(t.CITY_ID, ',', n.n), ',', -1) value
FROM Table1 t CROSS JOIN
(
SELECT a.N + b.N * 10 + 1 n
FROM
(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) a
,(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) b
ORDER BY n
) n
WHERE n.n <= 1 + (LENGTH(t.CITY_ID) - LENGTH(REPLACE(t.CITY_ID, ',', '')))
ORDER BY ID,value
フィドルのデモ
出力:
ID VALUE
1 12
1 16
1 17
1 18
1 35
2 12
2 16