How to auto-increment in PostgreSQL? [duplicate]

Answer 1

You are looking for a column with datatype Serial. See this page (bottom) for more information about that datatype.

So for example, your table definition could look like this:

CREATE TABLE yourtable (
    rank SERIAL NOT NULL,
    username VARCHAR(20) NOT NULL,
    password VARCHAR(50) NOT NULL
);

Answer 2

A Sequence can be created which will auto increment the value of rank column.

CREATE SEQUENCE rank_id_seq;

CREATE TABLE yourtable (
    rank INTEGER NOT NULL default nextval('rank_id_seq'),
    username VARCHAR(20) NOT NULL,
    password VARCHAR(50) NOT NULL
);

ALTER SEQUENCE rank_id_seq owned by yourtable.rank;

Answer 3

create table login (rank serial, username varchar(20), password varchar(20))

Serial datatype is what you want.