Drupal 7 - module.install文件架构错误

I have written below code in custom_notifications.install file.

When I am trying to enable that module its giving me error "The website encountered an unexpected error. Please try again later."

kindly help me with this.

function custom_notifications_schema() {

 $schema['custom_notification_log'] = array(
'fields' => array(
  'cnl' => array('type' => 'serial', 'unsigned' => TRUE, 'not null' => TRUE),
  'notification_type' => array('type' => 'varchar', 'length' => 64),
  'notification_type_id' => array('type' => 'int', 'unsigned' => TRUE),
  'uid' => array('type' => 'int', 'unsigned' => TRUE),
  'viewed_on' => array('type' => 'int', 'unsigned' => TRUE),
)
);
return $schema; 
}

A couple things to try:

1) Look at your dblog (Reports -> Recent log messages) for PHP errors providing more information.

2) Go to the Uninstall tab and see if your module is listed. If it is, then uninstall it, then attempt to re-install.

SERIAL is an alias for BIGINT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE. try removing the unsigned and not null keys for your cnl field