SQL> create table employee (name varchar2 (20));
Table created
SQL>  insert into employee values ('JOHN');
1 row inserted
SQL>  insert into employee values ('SCOTT');
1 row inserted
SQL>  insert into employee values ('CHARLES');
1 row inserted

SQL> select * from employee;

NAME
--------------------
JOHN
SCOTT
CHARLES

SQL> SELECT emp.NAME, estat.status
      from (SELECT NAME,
                   (CASE
                     WHEN NAME IN ('JOHN', 'MICHAEL') THEN
                      'Yes'
                     ELSE
                      'No'
                   END) status
              from employee) estat,
          employee emp
    where emp.name = estat.name
      and status = 'Yes';
	  
NAME                 STATUS
-------------------- ------
JOHN                 Yes

NAME                 STATUS
-------------------- ------
JOHN                 Yes
Michael               No

SELECT emp.name, CASE ...
FROM employee emp

SQL> with t_source (name) as
  2    (select 'JOHN'    from dual union
  3     select 'MICHAEL' from dual
  4    )
  5  select t.name,
  6         decode(e.rowid, null, 'No', 'Yes') status
  7  from t_source t left join employee e on t.name = e.name;

NAME    STATUS
------- ------
JOHN    Yes
MICHAEL No

SQL>

with t_source (name) as ( select column_value
  from table( sys.odcivarchar2list( 'JOHN', 'MICHAEL' ) )
  )
select ...

SQL> declare
  2    l_test boolean;
  3  begin
  4    l_test := true;
  5    dbms_output.put_line(case when l_test then 'TRUE' else 'FALSE' end);
  6    l_test := false;
  7    dbms_output.put_line(case when l_test then 'TRUE' else 'FALSE' end);
  8  end;
  9  /
TRUE
FALSE

PL/SQL procedure successfully completed.

SQL> declare
  2    l_test boolean;
  3    function tochar(p in boolean) return varchar2 is
  4    begin
  5      return case when l_test then 'TRUE' else 'FALSE' end;
  6    end;
  7  begin
  8    l_test := true;
  9    dbms_output.put_line(tochar(l_test));
 10    l_test := false;
 11    dbms_output.put_line(tochar(l_test));
 12  end;
 13  /
TRUE
FALSE

PL/SQL procedure successfully completed.

SQL> begin
  2  dbms_output.put_line(sys.diutil.bool_to_int(true));
  3  dbms_output.put_line(sys.diutil.bool_to_int(false));
  4  end;
  5  /
1
0

PL/SQL procedure successfully completed.

pdby1> set serverout on
pdby1> exec dbms_output.put_line(sys.diutil.bool_to_int(true))
1

PL/SQL procedure successfully completed.

pdby1> exec dbms_output.put_line(sys.diutil.bool_to_int(false))
0

PL/SQL procedure successfully completed.

pdby1> exec dbms_output.put_line(sys.diutil.bool_to_int(null))

PL/SQL procedure successfully completed.

pdby1>
pdby1>
pdby1> select * from dual where sys.diutil.bool_to_int(null) is null;

D
-
X

pdby1>

SQL> declare
  2    l_test boolean;
  3    function tochar(p in boolean) return varchar2 is
  4    begin
  5      return case when l_test then 'TRUE' when not l_test then 'FALSE' else null end;
  6    end;
  7  begin
  8    l_test := true;
  9    dbms_output.put_line('l_test is '||tochar(l_test));
 10    l_test := false;
 11    dbms_output.put_line('l_test is '||tochar(l_test));
 12    l_test := null;
 13    dbms_output.put_line('l_test is '||tochar(l_test));
 14  end;
 15  /
l_test is TRUE
l_test is FALSE
l_test is

PL/SQL procedure successfully completed.