dual table in Oracle?!

Anon

Hi, does anyone knoe, what the Dual Table is good for?!

I use it here for a trigger, that increments a field - I copied this example from an Oracle manual, but don't know what it does.

I've also seen this statement:

SELECT SYSDATE 2 FROM DUAL;

When I do a select * from dual, I get only: 'X'

thx

Anon

the dual table is just a dummy table with one record. It is good for things like testing the database connection, testing a new function, getting the sysdate, etc. You would run sql queries against it that do not need a table to run. For instance select sysdate from dual; to get the sysdate you don't need a table, but to run a SQL query you have to include a table.

Anon

Ahh ok thx. A slightly unlucky name for something, but who cares...

Do think this is a good way to auto-increment a field:

create sequence group_seq
start with 0
increment by 1
nomaxvalue;

create trigger group_trigger
before insert on dos_group
for each row
begin
select group_seq.nextval into :new.dos_group_id from dual;
end;
/

thx in advance, Thomas

Anon

put the group_seq.nextval right into your insert statement. Also I think there is another option 'nocache' that you may want to look into if you want a true sequence. Without it I think the sequence can skip numbers when the database is shutdown and restarted.

Anon

Hi Bill,

1.) I cant quit imagine, how you meant "put the group_seq.nextval right into your insert statement" Could you make an example?

2.) These things are the ony, why I'm always a bit afraid using sequences and triggers. I think they could be very dabgerous...
I forgot my Oracle CD today, do you know about a good pl/sql and Oracle resource on the web?

thx, Thomas

Anon

1) insert into table (field1,field2,autonumberfield3)
values ('text','moretext',group_seq.nextval);

2) try otn.oracle.com

Anon

Ok, thx a lot