Postgres Bigserial Datatype

Question

I am trying to create Postgres table with Bigserial data type as a promary key. Once I am creating the table the table definition is getting changed to bigint NOT NULL DEFAULT nextval('transactions.transaction_id_seq'::regclass), to this. Please let me know why this happenning?

Thanks In Advance, Somnath

Possible duplicate: Does Postgresql SERIAL work differently? — klin
– klin, Commented Apr 28, 2017 at 22:25

dhke · Accepted Answer · 2017-04-28 22:29:18Z

9

As noted in the documentation, serials are not "real" data types, but rather convenience wrappers. If you create a serial column, you automatically get

a new sequence ('tablename_columnname_seq`)
an integer column of the appropriate type that takes its default value from the sequence.
the setup for the column to use the sequence.

To quote:

The data types smallserial, serial and bigserial are not true types, but merely a notational convenience for creating unique identifier columns (similar to the AUTO_INCREMENT property supported by some other databases).

CREATE TABLE table (BIGSERIAL id PRIMARY KEY);

is the same as

CREATE SEQUENCE table_id_seq;
CREATE TABLE table (
   id bigint NOT NULL DEFAULT nextval('table_id_seq')
);
ALTER SEQUENCE table_id_seq OWNED BY table.id;

Which matches what you are getting.

answered Apr 28, 2017 at 22:29

dhke

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