Hi @Shambhu Rai
Thanks for your question.
Yes, it's possible to add constraints to a table even after it has been loaded with data.
However, this depends on the type of constraint being added.
Also, adding a constraint to a large table with existing data may take a long time to complete and may impact performance during the operation.
When you add a constraint to a table, the database engine validate that all existing data in the table conforms to the constraint.
It is generally recommended to add constraints to a table before loading data into it.
Thank you!