SQL & PL/SQL

SQL> with t as (
  2  select F_FLG, decode(min(min),max,to_char(max),min(min)||'-'||max) range,
  3  row_number() over(partition by f_flg order by max) rn from (
  4  select F_FLG, connect_by_root pr_no min, pr_no max
  5  from pr_temp
  6  where connect_by_isleaf=1
  7  connect by pr_no = prior pr_no+1 and F_FLG = prior f_flg)
  8  group by F_FLG, max)
  9  select F_FLG, ltrim(sys_connect_by_path(range,';'),';')  ranges
 10  from t 
 11  where connect_by_isleaf=1
 12  connect by rn = prior rn+1 and f_flg=prior f_flg
 13  start with rn=1;

     F_FLG RANGES
---------- ------------------------------
         0 11;13-15;17-18;20-22
         1 12;16;19;23-25

VARIABLE	target_f_flg	NUMBER
EXEC  :target_f_flg := 1;

WITH	got_grp_num	AS
(
	SELECT	  pr_no
	,	  pr_no - ROW_NUMBER () OVER (ORDER BY pr_no)	AS grp_num
	FROM	  pr_temp
	WHERE	  f_flg	= :target_f_flg
)
,	got_agg		AS
(
	SELECT	  MIN (pr_no)	AS min_pr_no
	,	  MAX (pr_no)	AS max_pr_no
	,	  ROW_NUMBER () OVER (ORDER BY grp_num)
				AS grp_seq
	FROM	  got_grp_num
	GROUP BY  grp_num
)
SELECT	LTRIM ( SYS_CONNECT_BY_PATH ( min_pr_no || CASE
							WHEN  min_pr_no != max_pr_no
							THEN  '-' || max_pr_no
						   END
				    , ';'
				    )
	      , ';'
	      )		AS result_txt
FROM	got_agg
WHERE	CONNECT_BY_ISLEAF	= 1
START WITH	grp_seq	= 1
CONNECT BY	grp_seq	= PRIOR grp_seq + 1
;

SQL> select ltrim(sys_connect_by_path(pr_no, ';'), ';')||';' pr_no
  2  ,      f_flg
  3  from ( select f_flg
  4         ,      case
  5                  when min(pr_no) = max(pr_no)
  6                  then to_char(min(pr_no))
  7                  else min(pr_no)||'-'||max(pr_no)
  8               end pr_no
  9         ,    row_number() over ( partition by f_flg order by min(pr_no) ) rn
 10         from ( 
 11                select f_flg 
 12                ,      pr_no
 13                ,      pr_no-row_number() over( partition by f_flg order by f_flg, pr_no ) rn    
          
 14                from ( select pr_no
 15                       ,      f_flg
 16                       from   pr_temp
 17                       order  by f_flg, pr_no
 18                     )
 19              )
 20         group by f_flg, rn
 21         order by f_flg
 22       )
 23  where connect_by_isleaf=1
 24  start with rn=1     
 25  connect by rn = prior rn+1     
 26         and f_flg = prior f_flg;

PR_NO                          F_FLG
------------------------- ----------
11;13-15;17-18;20-22;              0
12;16;19;23-25;                    1

col str for a35

select f_flg,substr(sys_connect_by_path(str,';'),2) as str
from (select f_flg,Row_Number() over(partition by f_flg order by dis) as rn,
      case count(*)
      when 1 then min(to_char(pr_no))
      else min(to_char(pr_no)) || '-' || max(to_char(pr_no)) end as str
        from (select pr_no,f_flg,
              pr_no-Row_Number() over(partition by f_flg order by pr_no) as dis
              from pr_temp)
      group by f_flg,dis)
where connect_by_IsLeaf = 1
start with rn=1
connect by prior f_flg = f_flg
      and  prior rn = rn-1;

F_FLG  STR
-----  --------------------
    0  11;13-15;17-18;20-22
    1  12;16;19;23-25