Specify Null values for the fields of a row type

The fields of a row-type column can contain NULL values. When you insert into or update a row-type field with a NULL value, you must cast the value to the data type of that field.

The following UPDATE statement shows how you might specify NULL values for particular fields of a named row-type column: 
UPDATE employee
   SET address = ROW(NULL::VARCHAR(20), 'Davis', 'CA',
   ROW(NULL::CHAR(5), NULL::CHAR(4)))::address_t)
   WHERE name = 'henry, john';
The following UPDATE statement shows how you specify NULL values for the street and zip fields of the address column for the student table.
UPDATE student
   SET address = ROW(NULL::VARCHAR(20), address.city,
   address.state, NULL::VARCHAR(9))
   WHERE s_name = 'henry, john';
Important: You cannot specify NULL values for a row-type column. You can only specify NULL values for the individual fields of the row type.