mysql将大量字符转换为字符

Question

英语不是我的母语；请原谅输入错误。

我使用5.5.38-MariaDB。 mysql语句：

SELECT CAST(11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
AS char);

我得到的结果是99999999999999999999999999999999999999999999999999999999999999999，为什么？

更新：

MariaDB [(none)]> SELECT CAST(199999999999999999999999999999999999999999999999999999999999999999999999999999999 AS char);
+-------------------------------------------------------------------------------------------------+
| CAST(199999999999999999999999999999999999999999999999999999999999999999999999999999999 AS char) |
+-------------------------------------------------------------------------------------------------+
| 199999999999999999999999999999999999999999999999999999999999999999999999999999999               |
+-------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

MariaDB [(none)]> SELECT CAST(1999999999999999999999999999999999999999999999999999999999999999999999999999999999 AS char);
+--------------------------------------------------------------------------------------------------+
| CAST(1999999999999999999999999999999999999999999999999999999999999999999999999999999999 AS char) |
+--------------------------------------------------------------------------------------------------+
| 99999999999999999999999999999999999999999999999999999999999999999                                |
+--------------------------------------------------------------------------------------------------+
1 row in set, 1 warning (0.01 sec)

MariaDB [(none)]> SHOW WARNINGS;
+---------+------+--------------------------------------------------------------+
| Level   | Code | Message                                                      |
+---------+------+--------------------------------------------------------------+
| Warning | 1916 | Got overflow when converting '' to DECIMAL. Value truncated. |
+---------+------+--------------------------------------------------------------+
1 row in set (0.00 sec)

Answer 1

1111...被解析为数字，尤其是DECIMAL(65, ...)。最大为65；因为东西比那还大，所以给了您65个9。它给了你一个警告（可能被忽略了）：

mysql> SELECT CAST(11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111 AS CHAR) AS too_big;
+-------------------------------------------------------------------+
| too_big                                                           |
+-------------------------------------------------------------------+
| 99999999999999999999999999999999999999999999999999999999999999999 |
+-------------------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> SHOW WARNINGS;                                                                               
+---------+------+---------------------------------------+
| Level   | Code | Message                               |
+---------+------+---------------------------------------+
| Warning | 1292 | Truncated incorrect DECIMAL value: '' |
+---------+------+---------------------------------------+
1 row in set (0.00 sec)

您希望得到什么？