SELECT  a.name,
		b.data,
		a.basiccd,
		a.status,
		c.name,
		b.txday,
		b.remark
from	ifapl a,
		wmmr b,
		psmr c,
		psmt d
where	b.mtelint = d.init and
		case 
			WHEN b.actionkey = '1' THEN
				 a.actno = b.data
			WHEN b.actionkey = '2' THEN
				 a.aano = b.data	 
		end; 		 

SQL> drop table faq;

Table dropped.

SQL> create table faq (id number, text1 varchar2(10), text2 varchar2(10));

Table created.

SQL> insert all
  2  into faq values (1, 'One', 'enO')
  3  into faq values (2, 'Two', 'owT')
  4  into faq values (3, 'Three', 'eerhT')
  5  into faq values (4, 'Four', 'ruoF')
  6  select 1 from dual;

4 rows created.

SQL> 
SQL> declare
  2    l_variable varchar2(10);
  3    l_result   number;
  4  begin
  5    l_variable := 'One';
  6    select id
  7    into   l_result
  8    from   faq
  9    where  1 = 1
 10    and    case when 1 = 2 then text2 = l_variable
 11  		   else text1 = l_variable
 12  	      end
 13    ;
 14    dbms_output.put_line('Found text '||l_result);
 15  end;
 16  /
  and    case when 1 = 2 then text2 = l_variable
                                    *
ERROR at line 10:
ORA-06550: line 10, column 37:
PL/SQL: ORA-00905: missing keyword
ORA-06550: line 6, column 3:
PL/SQL: SQL Statement ignored


SQL> Prompt The correct way:
The correct way:
SQL> declare
  2    l_variable varchar2(10);
  3    l_result   number;
  4  begin
  5    l_variable := 'One';
  6    select id
  7    into   l_result
  8    from   faq
  9    where  1 = 1
 10    and    l_variable = case when 1 = 2 then text2
 11  				else text1
 12  			   end
 13    ;
 14    dbms_output.put_line('Found text '||l_result);
 15  end;
 16  /
Found text 1

PL/SQL procedure successfully completed.

SQL> 
SQL> spool off