How create a serial field in a postgresql query? - postgresql

Question

In postgresql update/insert are very slow. So often is faster create a new table with the new field/row and then replace the old table
The thing is I need an autonumeric so in this case I had to create the table first and do the insert later.
Is there a way create an autonumeric field in the select so I can use
CREATE TABLE source.road_nodes AS
SELECT serial_field, node
instead of CREATE TABLE + INSERT.
CREATE TABLE source.road_nodes (
node_id serial,
node TEXT
);
INSERT INTO source.road_nodes (node)
SELECT DISTINCT node
FROM
(
SELECT DISTINCT node_begin AS node
FROM source.vzla_rto
) as node_pool;

Answer 1

In a way this is possible. You can take advantage of the fact that as the PostgreSQL documentation - 8.1.4. Serial Types states:
CREATE TABLE tablename (
colname SERIAL
);
is equivalent to specifying:
CREATE SEQUENCE tablename_colname_seq;
CREATE TABLE tablename (
colname integer NOT NULL DEFAULT nextval('tablename_colname_seq')
);
ALTER SEQUENCE tablename_colname_seq OWNED BY tablename.colname;
Creating a sequence separately and making the next value the default for the column you effectively make it a SERIAL column.
CREATE SEQUENCE road_nodes_node_id_seq;
CREATE TABLE road_nodes AS
SELECT DISTINCT ON (node) nextval('road_nodes_node_id_seq') AS node_id, node FROM vzla_rto;
ALTER TABLE road_nodes ALTER node_id SET NOT NULL, ALTER COLUMN node_id SET DEFAULT nextval('road_nodes_node_id_seq');
You could keep the sequence and just reset it to one when you would recreate the table.
I wouldn't say that this is an elegant way however and probably the easiest way is just to create the table separately.