create table mytable (
col1 number primary key,
col2 number,
col3 number not null
);
table MYTABLE created.
select table_name, column_name, nullable
from user_tab_cols where table_name = 'MYTABLE';
TABLE_NAME COLUMN_NAME NULLABLE
------------------------------ ------------------------------ --------
MYTABLE COL1 N
MYTABLE COL2 Y
MYTABLE COL3 N
Så nej, du behöver inte ange primärnyckelkolumner som NOT NULL.