Subtype normalization Data Type

Subtype is a type alias. If you want to change it, you only need to modify the definition of one place. Code No changes required
Maybe we are used to variables to represent unknown, but we are not used to variables to represent variable types.
Subtype plays a role in this way. It can use a new type variable to represent a known type.
If the variable you define is likely to need to change the variable type, using subtype can greatly reduce the amount of modification to your code.
There are many benefits, such as reusing, reducing dependencies between modules, and reducing maintenance costs.
For example,
Assume that I have a table: book, which has a field: page_count. The type is number (2)
Now I want to write Program To display the pages of all books I have currently written.
I can write it like this:
Declare
Rochelle total book. page_count % type;
This is fine, but what if all my pages exceed 100?
I can also write:
Declare
Rochelle total number (10 );
This is a hard coding method, and think is annoying.
This does not work either? That doesn't work either? How are you doing? Haha ....
In fact, we can do this:
Create or replace package pkg_book
As
Subtype total_count is number (10 );
End pkg_book;
Then,
Declare
Rochelle total pkg_book.total_count;