Question

5. MySQL(5.1.41-3ubuntu12.10-log)似乎在使用和开发(大于)和(以下)进行细化比较方面取得了可预见的成果:

select "a" > "a", "a" > "b", "b" > "a", "ab" > "aa", "ab" > "aabbbb";
+-----------+-----------+-----------+-------------+-----------------+
| "a" > "a" | "a" > "b" | "b" > "a" | "ab" > "aa" | "ab" > "aabbbb" |
+-----------+-----------+-----------+-------------+-----------------+
|         0 |         0 |         1 |           1 |               1 | 
+-----------+-----------+-----------+-------------+-----------------+

并且似乎还利用了关键因素:

explain select productcode from products where productcode <  no ; 
+----+-------------+----------+-------+-----------------+------+---------+------+------+--------------------------+
| id | select_type | table    | type  | possible_keys   | key  | key_len | ref  | rows | Extra                    |
+----+-------------+----------+-------+-----------------+------+---------+------+------+--------------------------+
|  1 | SIMPLE      | products | range | productcode,ppp | ppp  | 34      | NULL |  432 | Using where; Using index |
+----+-------------+----------+-------+-----------------+------+---------+------+------+--------------------------+

这似乎没有记录——它是否是一个可靠的跨平台特征?

Answer 1

我认为有一些 go,你可以在这里查看一些细节的文件:

http://dev.mysql.com/doc/refman/5.5/en/comparison-operators.html

If your fields have null values too, you should also take a look at null-safe comparision operator: http://dev.mysql.com/doc/refman/5.0/en/comparison-operators.html#operator_equal-to

例如:

mysql> select "a" > "a ", "A" > "a" , "aB"  > "ab" , "a" >= NULL , "a" <=> NULL ;
+------------+-----------+--------------+-------------+--------------+
| "a" > "a " | "A" > "a" | "aB"  > "ab" | "a" >= NULL | "a" <=> NULL |
+------------+-----------+--------------+-------------+--------------+
|          0 |         0 |            0 |        NULL |            0 |
+------------+-----------+--------------+-------------+--------------+

Answer 2

这些比较很常见。我确信,将体积与面值相比较,或像支持交叉面形的其他编码。我拿不出任何资源支持它。这很可能是比较内部的扼杀(以分类和分类)。我预计,这是一个主要特点。

Answer 3

<>光:<> 之所以可以预测,是因为将所涉数值分类为collation(s)。

About comparison in general

从MySQL类转换 docs,“比较业务的转变”:

如果比较行动中的两个论点都很明确,它们是,而后称“strong”。

www.un.org/Depts/DGACM/index_spanish.htm 与之相比,是指所涉数值/栏的collation(s)的分类算法。

About multiple collations involved

如果对与不同串通的两条歌剧(栏目,字面......)进行对比,那么会如何? 见MySQL colation coersion 。

About comparison in general

About multiple collations involved

友情链接