Oracle adds a primary key to the table and makes the ID self-increment

1, about the primary key: the construction of the table when the specified primary key words can:
CREATE TABLE Test (
 ID Number (6) primary key,
Name VARCHAR2 (30)
);
If you want to increase the primary KEY constraint for a table that has already been built, you would like the syntax:
ALTER TABLE TEST add constraint pk_id primary key (ID); 
Where add constraint and primary key are keywords, pk_id is the primary key name, custom amount, as long as you do not repeat.

2, about the ID self-increment function, is also very simple, and more flexible.
(1) First set up a sequence (that is, each time the query will automatically increment the value of the never-repeated object, such as 1 or each time plus 10). Grammar:
CREATE Sequence sequence Name
[INCREMENT by N]--Each time you add a few
[Start with n]-sequence from several beginnings
[{Maxvalue/minvalue n| Nomaxvalue}]--limit of minimum and maximum value
Like whatCREATE sequence s_test start  with 1 increment  by 1;--that is, a sequence that starts from 1 and adds 1 each time.
When you access a sequence, use the sequence name. Nextval syntax.

For example, for the table above, if you want the ID field to implement self-increment. Each time you insert a record, use a syntax similar to the following (provided the table and sequence are already built).
INSERT into test values (S_test.nextval, ' Zhang San ');

Of course, you can also automatically, to insert operations on the table, to create a trigger, whenever there is data inserted, the trigger automatically modifies the ID value to the new value of the sequence, so that the self-increment ID function is fully implemented. But there is no need for that. Because if the trigger is built more, it is sometimes confusing and difficult to manage.

Oracle adds a primary key to the table and makes the ID self-increment