ORA-06512:exact fetch returns more than requested number of rows

While running the below procedure I am getting the below error

Error report:
ORA-01422: exact fetch returns more than requested number of rows
ORA-06512: at "my_db.CREATE_CTAB_FILE", line 51
ORA-06512: at line 2
01422. 00000 -  "exact fetch returns more than requested number of rows"
*Cause:    The number specified in exact fetch is less than the rows returned.
*Action:   Rewrite the query or change number of rows requested

Could you please suggest me how I could assign fetched data into a variable? I suspect variable (lnbuf) of data type varchar2 is not accepting row fetched by the select statement. Please help me in solving this error

create or replace 
PROCEDURE CREATE_CTAB_FILE (f_ctab_id IN T_WN_CTAB_str.wn_ctab_id%type,
                                P_SYN_DIR in varchar2,
                                p_user    IN varchar2)

is 
FILEHANDLER WN_DB_UTL_FILE.FILE_TYPE;
LNBUF varchar2(4000) := null;
--cast(lnbuf as char(4000));
--LNBUF clob;

v_file     varchar2(256);
V_DATA_LOG varchar2(256);
V_WN_COUNTRY T_WN_CTAB_STR.WN_COUNTRY%type;
V_H_L varchar2(256);


BEGIN


for CTAB_REC in 
(select distinct WN_COUNTRY, WN_PRHB_DATE
from t_wn_ctab_h 
where wn_ctab_id =f_ctab_id)

loop

v_wn_country:=ctab_rec.wn_country;

--bkk_solution.wn_insert_res_log('create_ctab', NULL, NULL, help_rec.wn_cty,    help_rec.wn_vers_sol, 'START', p_cty);

v_file:=v_wn_country||'_CTAB'||'.txt';

fileHandler := WN_DB_UTL_FILE.FOPEN(P_SYN_DIR,V_FILE,'W');
--p_file_id := fileHandler.id;

lnbuf := ('#' || rpad(' ',42,' ') ||'V3.4.5'||rpad(' ',197,' ') ||            '000000000000000000000000000'||to_char(sysdate,'YYYYMMDD')||     to_char(ctab_rec.WN_PRHB_DATE,'YYYYMMDD') ||rpad(' ',48,' ')|| '1');   -- '<html>' -Tag ausgeben
WN_DB_UTL_FILE.PUTF(fileHandler, lnbuf);
 Loop
  LNBUF   := NULL ;

   SELECT (   CAST ('LT01' AS CHAR (8))
       || CAST (REC.WN_COUNTRY AS CHAR (3))
       || CAST (rec.WN_NORMSSNR_WW AS CHAR (32))
       || CAST (REC.WN_SOFTWARE AS CHAR (7))
       || CAST (REC.WN_NORMSSNR AS CHAR (32))
       || RPAD (' ', 32, ' ')
       || CAST (REC.WN_NAME_WW AS CHAR (16))
       || CAST (REC.WN_NAME AS CHAR (16))
       || CAST (REC.WN_NORMBYTE AS CHAR (6))
       || CAST ('0' AS CHAR (3))
       || CAST ('ST' AS CHAR (2))
       || RPAD (' ', 70, ' ')
       || CAST ('ST' AS CHAR (3))
       || RPAD (' ', 60, ' ')
       || TO_CHAR (rec.WN_FOD, 'YYYYMMDD')
       || TO_CHAR (rec.WN_LOD, 'YYYYMMDD'))
 INTO lnbuf
 FROM t_wn_ctab_str rec
WHERE rec.wn_ctab_id = 1234;
WN_DB_UTL_FILE.PUTF(fileHandler, lnbuf); 
end LOOP;
WN_DB_UTL_FILE.FCLOSE(fileHandler);
end LOOP; 
END CREATE_CTAB_FILE ;

Solution

As suggested by the error, and explained below that your select query is returning more than 1 rows and you are trying to store that in a variable, which is cuasing the issue. Change your loop as below:

for rec in (
               SELECT (   CAST ('LT01' AS CHAR (8))
                   || CAST (REC.WN_COUNTRY AS CHAR (3))
                   || CAST (rec.WN_NORMSSNR_WW AS CHAR (32))
                   || CAST (REC.WN_SOFTWARE AS CHAR (7))
                   || CAST (REC.WN_NORMSSNR AS CHAR (32))
                   || RPAD (' ', 32, ' ')
                   || CAST (REC.WN_NAME_WW AS CHAR (16))
                   || CAST (REC.WN_NAME AS CHAR (16))
                   || CAST (REC.WN_NORMBYTE AS CHAR (6))
                   || CAST ('0' AS CHAR (3))
                   || CAST ('ST' AS CHAR (2))
                   || RPAD (' ', 70, ' ')
                   || CAST ('ST' AS CHAR (3))
                   || RPAD (' ', 60, ' ')
                   || TO_CHAR (rec.WN_FOD, 'YYYYMMDD')
                   || TO_CHAR (rec.WN_LOD, 'YYYYMMDD'))  col1           
             FROM t_wn_ctab_str rec
            WHERE rec.wn_ctab_id = 1234 )
loop

LNBUF   := NULL ;

LNBUF := rec.col1;   

 WN_DB_UTL_FILE.PUTF(fileHandler, lnbuf); 

end LOOP;