DB 종류에 따라, 버전에 따라, 쿼리 문법이 달라질 텐데요.
DB 종류 및 버전을 알려주세요.

WITH t AS
(
SELECT 1 idx, '1' v FROM dual
UNION ALL SELECT  2, '1,10'              FROM dual
UNION ALL SELECT  3, '1,2'               FROM dual
UNION ALL SELECT  4, '1,2,3'             FROM dual
UNION ALL SELECT  5, '1,2,3,4'           FROM dual
UNION ALL SELECT  6, '1,2,3,4,5'         FROM dual
UNION ALL SELECT  7, '1,2,3,4,5,6'       FROM dual
UNION ALL SELECT  8, '1,2,3,4,5,6,7'     FROM dual
UNION ALL SELECT  9, '1,2,3,4,5,6,7,8'   FROM dual
UNION ALL SELECT 10, '1,2,3,4,5,6,7,8,9' FROM dual
UNION ALL SELECT 11, '2,3,4,5,6,7'       FROM dual
UNION ALL SELECT 12, '2,3,4,6,20'        FROM dual
UNION ALL SELECT 13, '2,3,4,6,7'         FROM dual
UNION ALL SELECT 14, '2,3,4,6,7,8'       FROM dual
UNION ALL SELECT 15, '2,3,4,6,8'         FROM dual
UNION ALL SELECT 16, '2,3,4,6,9'         FROM dual
UNION ALL SELECT 17, '2,3,4,7'           FROM dual
)
SELECT lv
     , COUNT(idx) cnt
  FROM (SELECT LEVEL lv FROM dual CONNECT BY LEVEL <= 20) a
  LEFT OUTER JOIN t b
    ON INSTR(','||v||',', ','||lv||',') > 0
 GROUP BY lv
 ORDER BY lv
;