How can Oracle modify a field to be not null?

To make a field in Oracle database not nullable, you can use the ALTER TABLE statement.

The grammar is as follows:

ALTER TABLE table_name MODIFY column_name datatype NOT NULL;

Among them, table_name is the name of the table to be modified, column_name is the name of the column to be modified, and datatype is the data type of the column.

For example, to change the field named email in the table named employees to be non-nullable, the following statement can be executed:

ALTER TABLE employees MODIFY email VARCHAR2(100) NOT NULL;

This will change the data type of the email field to VARCHAR2 and set it as not null. Data types and field names can be modified as needed based on actual requirements.