Impossible WHERE in explain

[Krishna Chandra Prajapati]

Hi,

In the query below explain gives 'Impossible WHERE noticed after'. what does
this mean.

CREATE TABLE `user_cookie` (
  `user_id` decimal(22,0) NOT NULL default '0',
  `param` varchar(128) NOT NULL default '',
  `value` varchar(128) default NULL,
  PRIMARY KEY  (`user_id`,`param`),
    CONSTRAINT `fk_user_cookie` FOREIGN KEY (`user_id`) REFERENCES
`user_info` (`user_id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB DEFAULT CHARSET=latin1

   SELECT VALUE  FROM user_cookie  WHERE USER_ID = '10538485' AND PARAM =
'TIMEOUT'    table |type |possible_keys |key | ken_len|ref | rows|  1
|SIMPLE | | | | | |Impossible WHERE noticed afte
-- 
Krishna Chandra Prajapati