Oracle SQL Questions

Hi

I am two questions about Oracle SQL.

1. I find that i can modify a column to "NOT NULL" even the column is the primary key of the table. What is the intention? Is it used in case of complex primary key?
2. What is the different of the following SQL statements.
3. alter table emp modify (ename not null);
4. alter table emp add constraint xemp check (ENAME IS NOT NULL); I find that "NOT NULL" is not shown when "desc emp" in the <b> case.

Morris
morriswg_at_netvigator.com Received on Fri Feb 12 1999 - 12:57:53 CST