Update to equivalent SQL in 8.1.4. Serial Types

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Page: https://www.postgresql.org/docs/11/datatype-numeric.html
Description:

In 8.1.4. Serial Types it says that 

CREATE TABLE tablename (
    colname SERIAL
);

is equivalent to

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;

Since Postgres 10, the datatype of the automatically-created sequence
matches the datatype of the serial column. But the default type for
CREATE SEQUENCE remains as bigint. So the second block should start with
the line

CREATE SEQUENCE tablename_colname_seq AS INTEGER;