SQL & PL/SQL

Version : 11.2

Permanant employees get monthly salary , Contract employees get only commission.
Some permanant employees like PETER and JOHANN get both salary and Commission


I want to find the total amount paid to both permanent and non-permanent employees.

During the total calculation, for employees who get both salary and Commission like PETER and JOHANN, I want to ignore Commission and consider only Salary of them for total pay calculation.

ie. When computing the total amount paid to all these employees

    I want to ignore commision of 400 received by PETER 
    and
    I want to ignore commision of 1000 received by  JOHANN

ie. The Total paid amount will be: 18,500

create table pay_master (emp_type varchar2(50) , empname varchar2(50), salary number , comm number );


insert into pay_master values ( 'PERM', 'KAREN' , 2000, 0 );
insert into pay_master values ( 'PERM', 'HANS'  , 3000, 0 );
insert into pay_master values ( 'CONTRACT', 'KEITH'  , 0, 1000 );

insert into pay_master values ( 'CONTRACT', 'ABDUL'  , 0, 2000 );
insert into pay_master values ( 'PERM', 'KRISHNA'  , 1000, 0 );
insert into pay_master values ( 'CONTRACT', 'CHENG'  , 0, 1500 );
insert into pay_master values ( 'PERM', 'PETER'  , 5000, 400 );
insert into pay_master values ( 'PERM', 'JOHANN'  , 3000, 1000 );


col EMP_TYPE format a10
col EMPNAME format a10

SQL> select * From pay_master order by empname;

EMP_TYPE   EMPNAME        SALARY       COMM
---------- ---------- ---------- ----------
CONTRACT   ABDUL               0       2000
CONTRACT   CHENG               0       1500
PERM       HANS             3000          0
PERM       JOHANN           3000       1000           ---------------> Ignore this commision when calculating the total pay
PERM       KAREN            2000          0
CONTRACT   KEITH               0       1000
PERM       KRISHNA          1000          0
PERM       PETER            5000        400           ---------------> Ignore this commision when calculating the total pay

8 rows selected.

SQL> select EMPNAME , salary+comm from pay_master order by empname;

EMPNAME    SALARY+COMM
---------- -----------
ABDUL             2000
CHENG             1500
HANS              3000
JOHANN            4000
KAREN             2000
KEITH             1000
KRISHNA           1000
PETER             5400

8 rows selected.

SQL> select sum(salary+comm) from pay_master;

SUM(SALARY+COMM)
----------------
           19900


Expected output from the SQL with the above mentioned logic is 18500

How can I do this in SQL ? I think I can't use CASE statement here because CASE statement only works within one column. Right?