SQL loader that inserts data from CSV file into a table

You don't have to do anything special - just omit all these columns from the control file, here:

(Emp_id char, Dept char, Class integer, Subclass integer )

To illustrate it: sample table has only two columns:

SQL> create table test
  2  (emp_id number,
  3   dept_name varchar2(10));

Table created.

Control file's data contain some more data - talking about this:

1,A,some more data,123
2,B,not important,553
    ------------------
    no columns for this in the table

Control file itself:

LOAD DATA
INFILE *
REPLACE
INTO TABLE test
FIELDS TERMINATED BY ',' 
OPTIONALLY ENCLOSED BY '"'
TRAILING NULLCOLS
(
emp_id,
dept_name
)

BEGINDATA
1,A,some more data,123
2,B,not important,553

Loading session:

SQL> $sqlldr scott/tiger@orcl control=test45.ctl log=test45.log

SQL*Loader: Release 18.0.0.0.0 - Production on Čet Lis 27 12:55:34 2022
Version 18.5.0.0.0

Copyright (c) 1982, 2018, Oracle and/or its affiliates.  All rights reserved.

Path used:      Conventional
Commit point reached - logical record count 1
Commit point reached - logical record count 2

Table TEST:
  2 Rows successfully loaded.

Check the log file:
  test45.log
for more information about the load.

Result:

SQL> select * from test;

    EMP_ID DEPT_NAME
---------- ----------
         1 A
         2 B

SQL>

As you can see, everything is just fine.

If it were vice versa, i.e. you'd want to populate columns that don't exist in the CSV file, you'd use e.g. filler (but - as that's not your issue - forget it. Actually, remember it, maybe you'll need it later).