mysql int范围与最大值分析

在SQL语句中int代表你要创建字段的类型，int代表整型，11代表字段的长度。

    这个代表显示宽度
整数列的显示宽度与需要用多少个字符来显示该列数值，与该整数需要的存储空间的大小都没有关系，比如，不管设定了显示宽度是多少个字符，bigint都要占用8个字节。

    int是整型，(11)是指显示字符的长度，但要加参数的，最大为255，比如它是记录行数的id,插入10笔资料，它就显示00000000001 ~~~00000000010，当字符的位数超过11,它也只显示11位，如果你没有加那个让它未满11位就前面加0的参数，它不会在前面加0

声明整型数据列时，我们可以为它指定个显示宽度M(1~255)，如INT(5)，指定显示宽度为5个字符,如果没有给它指定显示宽度，MySQL会为它指定一个默认值。显示宽度只用于显示，并不能限制取值范围和占用空间，如：INT(3)会占用4个字节的存储空间，并且允许的最大值也不会是999,而是INT整型所允许的最大值。

MySQL有五种整型数据列类型，即TINYINT，SMALLINT，MEDIUMINT，INT和BIGINT。它们之间的区别是取值范围不同，存储空间也各不相同。
在整型数据列后加上UNSIGNED属性可以禁止负数，取值从0开始。

int范围

Type	Bytes	Minimum Value	Maximum Value
		(Signed/Unsigned)	(Signed/Unsigned)
<font face="NSimsun">TINYINT</font>	1	<font face="NSimsun">-128</font>	<font face="NSimsun">127</font>
		<font face="NSimsun">0</font>	<font face="NSimsun">255</font>
<font face="NSimsun">SMALLINT</font>	2	<font face="NSimsun">-32768</font>	<font face="NSimsun">32767</font>
		<font face="NSimsun">0</font>	<font face="NSimsun">65535</font>
<font face="NSimsun">MEDIUMINT</font>	3	<font face="NSimsun">-8388608</font>	<font face="NSimsun">8388607</font>
		<font face="NSimsun">0</font>	<font face="NSimsun">16777215</font>
<font face="NSimsun">INT</font>	4	<font face="NSimsun">-2147483648</font>	<font face="NSimsun">2147483647</font>
		<font face="NSimsun">0</font>	<font face="NSimsun">4294967295</font>
<font face="NSimsun">BIGINT</font>	8	<font face="NSimsun">-9223372036854775808</font>	<font face="NSimsun">9223372036854775807</font>
		<font face="NSimsun">0</font>	<font face="NSimsun">18446744073709551615</font>

下面为官网的说明

代码如下	复制代码
Be careful when considering ENUM('T','F') as "true binary". Example: CREATE TABLE `bits` ( `val` ENUM('T','F') NOT NULL ); mysql> INSERT INTO `bits` (`val`) VALUES ('W'), ('T'), ('F'); Query OK, 3 rows affected, 1 warning (0.00 sec) Records: 3 Duplicates: 0 Warnings: 1 mysql> SHOW WARNINGS;

+---------+------+------------------------------------------+| Level   | Code | Message                                  |+---------+------+------------------------------------------+| Warning | 1265 | Data truncated for column 'val' at row 1 |+---------+------+------------------------------------------+1 row in set (0.00 sec)

mysql> SELECT COUNT(DISTINCT val) FROM bits;

+---------------------+| COUNT(DISTINCT val) |+---------------------+|                   3 |+---------------------+1 row in set (0.00 sec)

Well, shouldn't a binary type have only two distinct values?
(Note that it isn't NULL.)

Explanation from manual (10.4.4. The ENUM Type):
-----
If you insert an invalid value into an ENUM (that is, a string not present in the list of permitted values), the empty string is inserted instead as a special error value. This string can be distinguished from a “normal” empty string by the fact that this string has the numeric value 0. More about this later