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非常抱歉，在尝试所有案例之前，我急忙发了一封邮件，向大家说声抱歉！根据您的回答，我尝试并推翻了之前的想法。随着位数的变化，我很困惑。我没有测试多少位数是正常的，但我相信这个例子应该可以解释它。字符串类型与数字类型比较时，当位数大于某个值时，只返回与要查询的位数相同的结果，但有两种情况。其他数字一样吗？我没有一一尝试。想了解是什么原因造成的，隐式类型转换还是什么？

  CREATE TABLE `user` (
    `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
    `name` varchar(20) CHARACTER SET latin1 DEFAULT NULL,
    `simid` varchar(50) CHARACTER SET latin1 NOT NULL DEFAULT '',
    PRIMARY KEY (`id`)
    ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

    INSERT INTO `user` (`id`, `name`, `simid`)
    VALUES
    (1, 'ccc', '6441760021201308940'),
    (3, 'bb', '6441760021201308941'),
    (4, 'bb', '6441760021201308942');
    
    select * from user where simuid = 6441760021201308940;
    result：
    1 ccc 6441760021201308940
    3 bb 6441760021201308941
    4 bb 6441760021201308942
    
    but ：select * from user where simuid = '6441760021201308940';
    result：
    1 ccc 6441760021201308940

    mysql> select * from user;
    +------+------+------------------------+
    | id   | name | simid                  |
    +------+------+------------------------+
    |    5 | ccc  | 6441760021201307159    |
    |    6 | ccc  | 6441760021201307160    |
    |    7 | ccc  | 6441760021201307001    |
    |    8 | ccc  | 6441760021201307000    |
    |    9 | qqq  | 6441760021201308159    |
    |   10 | sss  | 6441760021201308160    |
    |   12 | jjj  | 641760021201308162     |
    |   13 | sss  | 6441760021201308161    |
    |   14 | jjj  | 6417600212013081620    |
    |   15 | sss  | 64417600212013081610   |
    |   21 | zzz  | 6441760021201308970    |
    |   51 | ccc  | 6441760021201308940    |
    |   52 | ddd  | 6441760021201308945    |
    |   53 | bb   | 6441760021201308941    |
    |   54 | bb   | 6441760021201308942    |
    |   55 | eee  | 6441760021201308946    |
    |  100 | sss  | 6441760021201308161000 |
    |  101 | jjj  | 641760021201308162000  |
    |  200 | sss  | 6441760021201308168000 |
    |  201 | jjj  | 6441760021201308169000 |
    | 1000 | aaa  | 64410                  |
    | 1001 | bbb  | 64411                  |
    +------+------+------------------------+
    22 rows in set (0.00 sec)

    select * from user where simid = 6441760021201307159;
        +----+------+---------------------+
        | id | name | simid               |
        +----+------+---------------------+
        |  5 | ccc  | 6441760021201307159 |
        |  6 | ccc  | 6441760021201307160 |
        |  9 | qqq  | 6441760021201308159 |
        | 10 | sss  | 6441760021201308160 |
        +----+------+---------------------+

mysql> select * from user where simid = 6441760021201308160000;
+-----+------+------------------------+
| id  | name | simid                  |
+-----+------+------------------------+
| 100 | sss  | 6441760021201308161000 |
| 200 | sss  | 6441760021201308168000 |
| 201 | jjj  | 6441760021201308169000 |
+-----+------+------------------------+
3 rows in set (0.01 sec)
mysql> select * from user where simid = 6441760021201308160;
+----+------+---------------------+
| id | name | simid               |
+----+------+---------------------+
|  5 | ccc  | 6441760021201307159 |
|  6 | ccc  | 6441760021201307160 |
|  9 | qqq  | 6441760021201308159 |
| 10 | sss  | 6441760021201308160 |
+----+------+---------------------+
4 rows in set (0.01 sec)

mysql> select * from user where simid = 6441760021201308161;
+----+------+---------------------+
| id | name | simid               |
+----+------+---------------------+
| 13 | sss  | 6441760021201308161 |
| 21 | zzz  | 6441760021201308970 |
| 51 | ccc  | 6441760021201308940 |
| 52 | ddd  | 6441760021201308945 |
| 53 | bb   | 6441760021201308941 |
| 54 | bb   | 6441760021201308942 |
| 55 | eee  | 6441760021201308946 |
+----+------+---------------------+
7 rows in set (0.00 sec)
4

1 回答 1

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问题是您尝试比较的VARCHAR和值被 MySQL 转换为数字，如12.3 表达式评估中的类型转换中所定义：INTEGERFLOAT

  • 在所有其他情况下，参数作为浮点（实）数进行比较。例如，字符串和数字操作数的比较是作为浮点数的比较进行的。

他们甚至有一个显示您的问题的示例：

为了说明，只有以下比较中的第一个比较相等的值，但两个比较都返回 true (1)：

mysql> SELECT '9223372036854775807' = 9223372036854775807;
       -> 1
mysql> SELECT '9223372036854775807' = 9223372036854775806;
       -> 1

解决方法很简单：不要比较VARCHAR和INTEGER值。或者您可以使用CAST()上述文档中提到的功能。

于 2020-10-17T09:38:20.947 回答