declare x number;
select count(*) into x from dba_tab_columns where table_name = 'My_Table_Name' and (column_name = 'ORDER_NUM' or column_name='DATE');
If the number output by X is the same as the number of columns you listed in the where clause above, they all exist. If X is less than the number of columns you listed, some of them don't exist.
Note: I used dbms_output.put_line solely to display the output for your use in SQL*PLUS. You could use this code in a procedure and test X with code rather than displaying it. Use capitals when searching the data dictionary for objects by name.
There is a possibility it will give the wrong output.
1.You have to mention the owner,as dba_tab_columns holds for all the users, if the same table exists in two users you will get the output different than what you expect