Query in SQL statement

Am trying to port a mysql statement to postgres.

Please help me in finding the error in this,


CREATE SEQUENCE ai_id;
CREATE TABLE badusers (
  id int DEFAULT nextval('ai_id') NOT NULL,
  UserName varchar(30),
  Date  datetime DEFAULT '0000-00-00 00:00:00' NOT NULL,
  Reason varchar(200),
  Admin varchar(30) DEFAULT '-',
  PRIMARY KEY (id),
  KEY UserName (UserName),
  KEY Date (Date)
);


Am always getting foll. Errors,

ERROR:  relation "ai_id" already exists
ERROR:  syntax error at or near "(" at character 240

Thanks,
Rajesh R