MySQL中int类型详解

    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)
TINYINT 1 -128 127
    0 255
SMALLINT 2 -32768 32767
    0 65535
MEDIUMINT 3 -8388608 8388607
    0 16777215
INT 4 -2147483648 2147483647
    0 4294967295
BIGINT 8 -9223372036854775808 9223372036854775807
    0 18446744073709551615

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