I do not understand what is wrong with this query? Query tool does not want to create a table in PostgreSQL.
CREATE TABLE article (
article_id bigint(20) NOT NUL
First the bigint(20) not null auto_increment will not work, simply use bigserial primary key. Then datetime is timestamp in PostgreSQL. All in all:
CREATE TABLE article (
article_id bigserial primary key,
article_name varchar(20) NOT NULL,
article_desc text NOT NULL,
date_added timestamp default NULL
);