标签:mysql comparison string-comparison
MySQL(5.1.41-3ubuntu12.10-log)似乎使用>给出了字符串比较的可预测结果. (大于)和< (少于):
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 |
+-----------+-----------+-----------+-------------+-----------------+
而且似乎也使用了键:
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 – 它是一个可靠的跨平台功能吗?
解决方法:
我认为有一些问题,您可以在这里查看文档以获取一些细节:
http://dev.mysql.com/doc/refman/5.5/en/comparison-operators.html
如果您的字段也具有空值,您还应该查看null-safe比较运算符:
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 |
+------------+-----------+--------------+-------------+--------------+
标签:mysql,comparison,string-comparison 来源: https://codeday.me/bug/20191001/1840556.html
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