Oracle Sequence starting with 2 instead of 1

Question

Unexpected behavior:

I am encountering strange behavior of Oracle sequences with 11g (works with 10g):

CREATE SEQUENCE test_sequence         


        

Answer 1

I can't reproduce on 11G, i.e. the table contains a 1 after following your steps.

However, it is debatable whether this should be considered an "issue", because sequences are never guaranteed to be gap-free. What START WITH guarantees is that the sequence will never return a value lower than the specified starting value - e.g. to avoid conflicts with existing data. I do agree however that what you are seeing is surprising and I would be interested to know the reason!

Answer 2

This is documented in the 11.2 SQL Language Reference where it says,

If you attempt to insert a sequence value into a table that uses deferred segment creation, the first value that the sequence returns will be skipped.

See the link in Jeffrey Kemp's answer for a My Oracle Support (Metalink) note and a workaround.

Answer 3

Use:

CREATE SEQUENCE SQ_SEQUENCE_NAME
    INCREMENT BY 1
    START WITH 1
    MINVALUE 0  -- This will ensure start at 1!
    MAXVALUE 99
    NOCYCLE
    NOCACHE
    ORDER;

Answer 4

I'd say the cause is this "undocumented feature". See My Oracle Support Document ID 1273858.1 (which is unfortunately behind a paywall and cannot be copied here).

Try it without deferred segment creation and see if the problem persists.