How do I Create an AutoIncrement on a Primary key Default

Question

I am new to Oracle and need to know how to create a table that uses an automatic incrementation on a primay key for it's default. I need the uniqueness automatically managed by the DBMS.. This activity is know as setting the Column (primary key with identity) in Ms-SQL..
Your help would be appreciated greatly....
Thanks....

Answer 1

you will have to create a sequence and a trigger
CREATE SEQUENCE <SEQUENCE NAME>
INCREMENT BY  1
START WITH  1
NOCACHE
/this sequence will guarantee that each requested number is unique
the trigger will select from this sequence and insert the obtained value in the new record
CREATE OR REPLACE TRIGGER <TRIGGER NAME>
BEFORE INSERT ON <TABLE NAME>
REFERENCING NEW AS NEW OLD AS OLD
FOR EACH ROW
    BEGIN
        select
            <SEQUENCE NAME>.nextval
        into
            :NEW.<COLUMN NAME>
        from
            dual;
    END;
[/CODE]
this will always take the value from the sequence, even if you already provided a value yourself
(otherwise you will first have to test if :NEW.<column name> is null, but I wouldn't do this for a key column.
if you need the generated key back for further processing (inserting it into a child table for example), you can use the returning clause on the insert statement
see the oracle documentation for more information about sequences, triggers and the returning clause
greetings
Freek D
I am new to Oracle and need to know how to create a table that uses an automatic incrementation on a primay key for it's default. I need the uniqueness automatically managed by the DBMS.. This activity is know as setting the Column (primary key with identity) in Ms-SQL..
Your help would be appreciated greatly....
Thanks....