CREATE TABLE OT_JOB_STAT ( JOB_NO VARCHAR2(12),JOB_STATUS VARCHAR2(12),JOB_EQUIP VARCHAR2(12),JOB_TYPE VARCHAR2(12))

insert into ot_job_stat ( JOB_NO ,JOB_STATUS ,JOB_EQUIP ,JOB_TYPE ) values ('0001','Open','CNC1','Prev')

insert into ot_job_stat ( JOB_NO ,JOB_STATUS ,JOB_EQUIP ,JOB_TYPE ) values ('0002','Close','CNC2','Brk')

select * from ot_job_stat where  (1 = 1 and :STATUS IS NULL) or (1 = 0 or JOB_STATUS = :STATUS ) 

JOB_NO	JOB_STATUS	JOB_EQUIP	JOB_TYPE
0001	Open	           CNC1	          Prev
0002	Close	           CNC2	          Brk

select * from ot_job_stat where  (1 = 1 and :STATUS IS NULL) or (1 = 0 or JOB_STATUS = :STATUS ) 
           and job_equip IN (:VAL1) )

--and the :val1 in ('CNC1')
 
JOB_NO	JOB_STATUS	JOB_EQUIP	JOB_TYPE
0001	Open	          CNC1	           Prev
0002	Close	          CNC2	           Brk

select * from ot_job_stat 
where (1 = 1 and :STATUS IS NULL) or (1 = 0 or JOB_STATUS = :STATUS)
  and job_equip IN (:VAL1);

select * from ot_job_stat 
where ((1 = 1 and :STATUS IS NULL) or (1 = 0 or JOB_STATUS = :STATUS))
--    ^                                                              ^
--    |                                                              |  these brackets!
  and job_equip IN (:VAL1);

   OR (1=0 OR job_equip LIKE NVL(:equip,'%')) 

insert INTO OT_JOB_STAT (
  JOB_NO      ,
  JOB_STATUS,
  JOB_EQUIP   ,
  JOB_TYPE   
)
VALUES(
'0003',
'Close',
'CNC3',
'Prev');

commit;

select * from ot_job_stat 
where ((1 = 1 and :STATUS IS NULL) or (1 = 0 or JOB_STATUS = :STATUS) and job_equip IN (:VAL1));

:status is null
:VAL1  = CNC1,CNC2

with the above parameters i am getting the below results which is wrong

JOB_NO	JOB_STATUS	JOB_EQUIP	JOB_TYPE
0001	Open	           CNC1	            Prev
0002	Close	           CNC2	             Brk
0003	Close	           CNC3	            Prev


Actaull it should filter only for CNC1 AND CNC2

JOB_NO	JOB_STATUS	JOB_EQUIP	JOB_TYPE
0001	Open	           CNC1	            Prev
0002	Close	           CNC2	             Brk

orclz> select * from ot_job_stat
  2  where ((1 = 1 and :STATUS IS NULL) or (1 = 0 or JOB_STATUS = :STATUS))
  3  and job_equip IN ('CNC1','CNC2');

JOB_NO       JOB_STATUS   JOB_EQUIP    JOB_TYPE
------------ ------------ ------------ ------------
0001         Open         CNC1         Prev
0002         Close        CNC2         Brk

orclz>

declare
	cnt number;
	var varchar2(32000);
	VAAL VARCHAR2(32500);
begin
cnt := Get_List_Element_Count('IP_REP_INFO.T_LIST_IN');
if cnt >= 1
	then
	var := null;
	for i in 1..cnt loop
		var := var||','||Get_List_Element_Value('IP_REP_INFO.T_LIST_IN',i);
			 VAAL :=  ''''||var||'''';
	end loop;


	:IP_REP_INFO.VAL := rtrim(substr(vaal, 2)); --This is the field which should be considered in In clause of query
	Else
		:IP_REP_INFO.VAL := nvl(:IP_REP_INFO.T_LIST_IN, -1);

end if;

end;

select * from ot_job_stat
  where ((1 = 1 and :STATUS IS NULL) or (1 = 0 or JOB_STATUS = :STATUS))
   and job_equip IN (CNC1,CNC2);

change automatically to


select * from ot_job_stat
  where ((1 = 1 and :STATUS IS NULL) or (1 = 0 or JOB_STATUS = :STATUS))
   and job_equip IN ('CNC1','CNC2');

SCOTT@orcl12c> -- table and data you provided:
SCOTT@orcl12c> CREATE TABLE OT_JOB_STAT
  2    (JOB_NO	    VARCHAR2(12),
  3  	JOB_STATUS  VARCHAR2(12),
  4  	JOB_EQUIP   VARCHAR2(12),
  5  	JOB_TYPE    VARCHAR2(12))
  6  /

Table created.

SCOTT@orcl12c> insert all
  2  into ot_job_stat (JOB_NO ,JOB_STATUS ,JOB_EQUIP ,JOB_TYPE)
  3    values ('0001','Open','CNC1','Prev')
  4  into ot_job_stat (JOB_NO ,JOB_STATUS ,JOB_EQUIP ,JOB_TYPE)
  5    values ('0002','Close','CNC2','Brk')
  6  into ot_job_stat (JOB_NO ,JOB_STATUS ,JOB_EQUIP ,JOB_TYPE)
  7    VALUES ('0003', 'Close', 'CNC3', 'Prev')
  8  select * from dual
  9  /

3 rows created.

SCOTT@orcl12c> -- variables:
SCOTT@orcl12c> VARIABLE status VARCHAR2(12)
SCOTT@orcl12c> VARIABLE val1   VARCHAR2(4000)
SCOTT@orcl12c> -- sample code to simulate generation of value for :val1:
SCOTT@orcl12c> DECLARE
  2    -- simulation of IP_REP_INFO.T_LIST_IN (skip next line):
  3    t_list_in SYS.ODCIVARCHAR2LIST := SYS.ODCIVARCHAR2LIST ('CNC1', 'CNC2');
  4    cnt	 NUMBER;
  5  BEGIN
  6    -- cnt := Get_List_Element_Count('IP_REP_INFO.T_LIST_IN');
  7    -- Use line above instead of line below.
  8    cnt := t_list_in.COUNT;
  9    FOR i IN 1..cnt LOOP
 10  	 -- :val1 := :val1 || Get_List_Element_Value('IP_REP_INFO.T_LIST_IN',i) || ',';
 11  	 -- Use line above instead of line below.
 12  	 :val1 := :val1 || t_list_in(i) || ',';
 13    END LOOP;
 14    :val1 := RTRIM (:val1, ',');
 15    DBMS_OUTPUT.PUT_LINE (:val1);
 16  END;
 17  /
CNC1,CNC2

PL/SQL procedure successfully completed.

SCOTT@orcl12c> -- str2tbl function by Tom Kyte from
SCOTT@orcl12c> -- http://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:110612348061
SCOTT@orcl12c> create or replace type myTableType as table of varchar2(255);
  2  /

Type created.

SCOTT@orcl12c> create or replace function str2tbl( p_str in varchar2 ) return myTableType
  2  as
  3  	 l_str	 long default p_str || ',';
  4  	 l_n	    number;
  5  	 l_data    myTableType := myTabletype();
  6  begin
  7  	 loop
  8  	     l_n := instr( l_str, ',' );
  9  	     exit when (nvl(l_n,0) = 0);
 10  	     l_data.extend;
 11  	     l_data( l_data.count ) := ltrim(rtrim(substr(l_str,1,l_n-1)));
 12  	     l_str := substr( l_str, l_n+1 );
 13  	 end loop;
 14  	 return l_data;
 15  end;
 16  /

Function created.

SCOTT@orcl12c> -- query:
SCOTT@orcl12c> SELECT *
  2  FROM   ot_job_stat
  3  WHERE  ((1 = 1 and :STATUS IS NULL)
  4  OR      (1 = 0 or JOB_STATUS = :STATUS))
  5  AND    job_equip IN
  6  	    (SELECT *
  7  	     FROM   TABLE (CAST (str2tbl (:val1) AS mytabletype)))
  8  /

JOB_NO       JOB_STATUS   JOB_EQUIP    JOB_TYPE
------------ ------------ ------------ ------------
0001         Open         CNC1         Prev
0002         Close        CNC2         Brk

2 rows selected.