Widening conversions

You do not need to use the convert function to specify a widening conversion. For example, since the Address2Line class is a subclass of the Address class, you can assign Address2Line values to Address data items. In the emps table, the home_addr column is an Address datatype and the mailing_addr column is an Address2Line datatype:

update emps
	set home_addr = mailing_addr
	where home_addr is null 

For the rows fulfilling the where clause, the home_addr column contains an Address2Line, even though the declared type of home_addr is Address.

Such an assignment implicitly treats an instance of a class as an instance of a superclass of that class. The runtime instances of the subclass retain their subclass datatypes and associated data.