Answer / srinu

U r correct Chandan.But one thing,what is that is if the
table contains some data at that time syntax for adding new
column to that table with notnull constraint is....

alter table table_name add column_name datatype default
value constraint constraint_name not null;

if we want 2 know which columns have which constraints then
the syntax is

select column_name,constraint_type
from user_cons_columns
where table_name='EMP';

Answer / chandan kumar

If table is empty (means no records are there) then we can
add the constraint.

alter table tablename add (col_name datatype not null)

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