(my_col in (1, 2, 3) or my_col is null)

decode(x(+), :a,0, :b,0, :c,0) = 0

SQL> select e.ename, e.deptno, d.deptno, d.dname  from scott.emp e, scott.dept d
  2  where d.deptno = e.deptno (+) and e.deptno (+) = 20
  3  /
 
ENAME      DEPTNO DEPTNO DNAME
---------- ------ ------ --------------
SMITH          20     20 RESEARCH
JONES          20     20 RESEARCH
SCOTT          20     20 RESEARCH
ADAMS          20     20 RESEARCH
FORD           20     20 RESEARCH
                      40 OPERATIONS
                      30 SALES
                      10 ACCOUNTING
 
8 rows selected
 
SQL> 

SQL> select e.ename, e.deptno, d.deptno, d.dname from scott.dept d left join scott.emp e
  2  on (d.deptno = e.deptno) and (e.deptno = 20)
  3  /
 
ENAME      DEPTNO DEPTNO DNAME
---------- ------ ------ --------------
SMITH          20     20 RESEARCH
JONES          20     20 RESEARCH
SCOTT          20     20 RESEARCH
ADAMS          20     20 RESEARCH
FORD           20     20 RESEARCH
                      40 OPERATIONS
                      30 SALES
                      10 ACCOUNTING
 
8 rows selected
 
SQL> 

SQL> select e.ename, e.deptno, d.deptno, d.dname from scott.dept d left join scott.emp e
  2  on (d.deptno = e.deptno) and (e.deptno in (20,30))
  3  /
 
ENAME      DEPTNO DEPTNO DNAME
---------- ------ ------ --------------
                      10 ACCOUNTING
SMITH          20     20 RESEARCH
JONES          20     20 RESEARCH
SCOTT          20     20 RESEARCH
ADAMS          20     20 RESEARCH
FORD           20     20 RESEARCH
ALLEN          30     30 SALES
WARD           30     30 SALES
MARTIN         30     30 SALES
BLAKE          30     30 SALES
TURNER         30     30 SALES
JAMES          30     30 SALES
                      40 OPERATIONS
 
13 rows selected
 
SQL> 

  1  select
  2   i.dep,dname
  3  from dept d,
  4   (select '10' dep from dual
  5    union all
  6    select '20' dep from dual
  7    union all
  8    select '50' dep from dual) i
  9* where d.deptno(+)=i.dep
SQL> /

DE DNAME
-- --------------
10 ACCOUNTING
20 RESEARCH
50

select substr( my_str, 
               instr(my_str,',',1, rownum) + 1, 
               instr(my_str,',',1, rownum + 1) -  instr(my_str,',',1, rownum) - 1
             ) as new_str
  from (select ','||ltrim(rtrim(:str,','),',')||',' as my_str from dual)
 connect by level <= length(ltrim(rtrim(my_str,','),',')) - length(replace(:str,',')) + 1

select substr( my_str, 
               instr(my_str,',',1, rownum) + 1, 
               instr(my_str,',',1, rownum + 1) -  instr(my_str,',',1, rownum) - 1
             ) as new_str
  from (select ','||ltrim(rtrim(:str,','),',')||',' as my_str from dual)
 connect by level <= length(ltrim(rtrim(my_str,','),',')) - length(replace(:str,',')) + 1

SELECT col1 from tab1
UNION
SELECT col2 from tab1
UNION 
SELECT col3 from tab1