SQL写法

SELECT col1,
         SUBSTR(MAX(SYS_CONNECT_BY_PATH(col2, '+')), 2) path
    FROM (SELECT col1,
                 col2,
                 LAG(col2, 1, NULL) OVER(PARTITION BY col1 ORDER BY col2) t_b
            FROM t1) tt
CONNECT BY PRIOR col2 = t_b
        AND PRIOR col1 = col1
   START WITH t_b IS NULL
   GROUP BY col1;