Question

有谁能告诉我为什么会发生以下情况，以及如何解决？

我有一个带有ORDER BY子句的MySQL查询，看起来像这样..

ORDER BY (did_voteup-did_votedown) DESC, did_voteup DESC

因此，它应按照“有效”评级对结果进行排序，如...

1st. 10 up - 1 down = 9 effective
2nd. 10 up - 5 down = 5 effective
3rd. 10 up - 7 down = 3 effective

然而，正如你在my page here上看到的那样，它是错误的，并且给了我这个......

1st. 1 up - 3 down = -2 effective
2nd. 16 up - 6 down = 10 effective
3rd. 15 up - 5 down = 10 effective

显然，第一名不应该在那里。

更多信息..

CREATE TABLE dictionary_definitions (
  did_id int(11) unsigned NOT NULL auto_increment,
  did_wordid int(11) unsigned NOT NULL default '0',
  did_userid int(11) unsigned NOT NULL default '0',
  did_status tinyint(1) unsigned NOT NULL default '0',
  did_date int(11) NOT NULL default '0',
  did_definition text,
  did_example text,
  did_votecheck int(11) NOT NULL default '0',
  did_voteup smallint(5) unsigned NOT NULL default '0',
  did_votedown smallint(5) unsigned NOT NULL default '0',
  PRIMARY KEY (did_id),
  KEY (did_wordid),
  KEY (did_userid)
) ENGINE=MyISAM;

SELECT a.did_id, a.did_userid, a.did_definition, a.did_example, 
    a.did_votecheck, a.did_voteup, a.did_votedown, b.user_name, b.user_extra8 
FROM dictionary_definitions AS a LEFT JOIN users AS b ON a.did_userid=b.user_id 
WHERE did_wordid=4 
ORDER BY (did_voteup-did_votedown) DESC, did_voteup DESC LIMIT 0, 5

Answer 1

这是一个众所周知的issue regarding subtraction from unsigned integers。

整数值之间的减法（其中一个是UNSIGNED类型）产生无符号结果默认。如果结果否则将是负面的，它就变成了最大整数值。如果启用了NO_UNSIGNED_SUBTRACTION SQL模式，则结果为负。

参考：Numeric Types

MySQL查询疯了吗？

1 个答案: