MySQL的数值类型
整数类型
整数类型包含TINYINT、SMALLINT、MEDIUMINT、INT、 BIGINT等。
存取范围
| 类型 | 存储大小 | 默认显示宽度（个） | 范围（有符号） | 范围（无符号） | 用途 | |
|---|---|---|---|---|---|---|
| TINYINT(m) | 1Byte | m：4 | -128 - 127 | 0 - 255 | 小整数值 | |
| SMALLINT(m) | 2Byte | m：6 | -32768 - 32767 | 0 - 65535 | 大整数值 | |
| MEDIUMINT(m) | 3Byte | m：9 | -8388608 - 8388607 | 0 - 16777215 | 大整数值 | |
| INT\ | INTEGER(m) | 4Byte | m：11 | -2147483648 - 2147483647 | 0 - 4294967295 | 大整数值 |
| BIGINT(m) | 8Byte | m：20 | -9233372036854775808 - 9223372036854775807 | 0 - 18446744073709551615 | 极大整数值 |
m为其显示宽度，在为字段设置 zerofill约束条件时有效，否则将不会填充满整个显示宽度。
可选约束
unsigned：使用无符号存储。
zerofill：显示宽度不够时使用0进行填充。
显示宽度
使用一切数值类型时，指定其宽度均是为其指定显示宽度，并非存入的限制宽度。
以下示例将演示为TINYINT类型设置设置了显示宽度后，当宽度不够时将以指定字符进行填充。
mysql> CREATE TABLE `test` (
-> `id` int(11) NOT NULL AUTO_INCREMENT,
-> `a` tinyint(4) unsigned zerofill DEFAULT NULL,
-> `b` smallint(6) unsigned DEFAULT NULL,
-> `c` mediumint(9) DEFAULT NULL,
-> `d` int(11) DEFAULT NULL,
-> `e` bigint(20) DEFAULT NULL,
-> PRIMARY KEY (`id`)
-> ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8 COLLATE=utf8_bin;
Query OK, 0 rows affected, 9 warnings (0.05 sec)mysql> desc test;
+-------+------------------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------------------------+------+-----+---------+----------------+
| id | int | NO | PRI | NULL | auto_increment |
| a | tinyint(4) unsigned zerofill | YES | | NULL | |
| b | smallint unsigned | YES | | NULL | |
| c | mediumint | YES | | NULL | |
| d | int | YES | | NULL | |
| e | bigint | YES | | NULL | |
+-------+------------------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)mysql> INSERT INTO `test` (`a`, `b`, `c`, `d`, `e`) VALUES ('1', '1', '1', '1', '1');
Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO `test` (`id`, `a`, `b`, `c`, `d`, `e`) VALUES ('3', '-1', '-1', '1', '1', '1');
ERROR 1264 (22003): Out of range value for column 'a' at row 1
mysql> INSERT INTO `test` (`a`, `b`, `c`, `d`, `e`) VALUES ('333', '333', '333', '333', '333');
ERROR 1264 (22003): Out of range value for column 'a' at row 1mysql> select * from test;
+----+------+------+------+------+------+
| id | a | b | c | d | e |
+----+------+------+------+------+------+
| 3 | 0001 | 1 | 1 | 1 | 1 |
+----+------+------+------+------+------+
1 row in set (0.00 sec)范围超出
当范围超出时则不允许存取，抛出异常。
浮点类型
浮点类型包括FLOAT、DOUBLE、DECIMAL。
存取范围
| 类型 | 存储大小 | 最大显示宽度（个） | 范围（有符号） | 范围（无符号） | 精确度 |
|---|---|---|---|---|---|
| FLOAT(m[,d]) | 4Bytes | m：255，d：30 | (-3.402 823 466 E+38，-1.175 494 351 E-38) - 0 | 0 - (1.175 494 351 E-38，3.402 823 466 E+38) | 点七位以内 |
| DOUBLE(m[,d]) | 8Bytes | m：255，d：30 | (-1.797 693 134 862 315 7 E+308，-2.225 073 858 507 201 4 E-308) - 0 | 0 - (2.225 073 858 507 201 4 E-308，1.797 693 134 862 315 7 E+308) | 点十五位以内 |
| DECIMAL(m[,d]) | m+2（如果m| m：65，d：30 |
取决于m,d（m范围（1-65），d范围（0-30）） |
取决于m,d（m范围（1-65），d范围（0-30）） |
绝对精准 |
|
m为其整数部分显示个数，n为其小数部分显示个数。
DECIMAL底层由字符串进行存储，故精度不会出现偏差，也被称为定点类型。
精度问题
mysql> CREATE TABLE `test` (
-> `id` INT NOT NULL,
-> `a` FLOAT NULL,
-> `b` DOUBLE NULL,
-> `c` DECIMAL NULL,
-> PRIMARY KEY (`id`));
Query OK, 0 rows affected (0.02 sec)mysql> desc test;
+-------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| a | float | YES | | NULL | |
| b | double | YES | | NULL | |
| c | decimal(10,0) | YES | | NULL | |
+-------+---------------+------+-----+---------+-------+
4 rows in set (0.01 sec)INSERT INTO `test` (`id`, `a`, `b`,`c`) VALUES ('1', '3.1415', '3.14159','3.14159');
INSERT INTO `test` (`id`, `a`, `b`,`c`) VALUES ('2', '1.1111111111111111', '1.1111111111111111','1.1111111111111111');mysql> select * from test;
+----+---------+--------------------+------+
| id | a | b | c |
+----+---------+--------------------+------+
| 1 | 3.1415 | 3.14159 | 3 |
| 2 | 1.11111 | 1.1111111111111112 | 1 |
+----+---------+--------------------+------+
2 rows in set (0.01 sec)mysql> alter table test modify `c` DECIMAL(65,30) NULL;
Query OK, 2 rows affected (0.13 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> desc test;
+-------+----------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| a | float | YES | | NULL | |
| b | double | YES | | NULL | |
| c | decimal(65,30) | YES | | NULL | |
+-------+----------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
mysql> select * from test;
+----+---------+--------------------+----------------------------------+
| id | a | b | c |
+----+---------+--------------------+----------------------------------+
| 1 | 3.1415 | 3.14159 | 3.000000000000000000000000000000 |
| 2 | 1.11111 | 1.1111111111111112 | 1.000000000000000000000000000000 |
+----+---------+--------------------+----------------------------------+
2 rows in set (0.00 sec)
mysql> INSERT INTO `test` (`id`, `a`, `b`,`c`) VALUES ('3', '1.1111111111111111', '1.1111111111111111','1.1111111111111111');
Query OK, 1 row affected (0.00 sec)
mysql> select * from test;
+----+---------+--------------------+----------------------------------+
| id | a | b | c |
+----+---------+--------------------+----------------------------------+
| 1 | 3.1415 | 3.14159 | 3.000000000000000000000000000000 |
| 2 | 1.11111 | 1.1111111111111112 | 1.000000000000000000000000000000 |
| 3 | 1.11111 | 1.1111111111111112 | 1.111111111111111100000000000000 |
+----+---------+--------------------+----------------------------------+
3 rows in set (0.00 sec)位类型
BIT(M)可以用来存放多位二进制数，M范围从1~64，如果不写默认为1位。
注意：对于位字段需要使用函数读取
bin()显示为二进制
hex()显示为十六进制
mysql> create table `test`(num bit);
Query OK, 0 rows affected (0.03 sec)
mysql> desc test;
+-------+--------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------+------+-----+---------+-------+
| num | bit(1) | YES | | NULL | |
+-------+--------+------+-----+---------+-------+
1 row in set (0.01 sec)
mysql> insert into `test`(num) values (1);
Query OK, 1 row affected (0.01 sec)
mysql> select * from test;
+------------+
| num |
+------------+
| 0x01 |
+------------+
1 row in set (0.00 sec)
mysql> select bin(num),hex(num) from test;
+----------+----------+
| bin(num) | hex(num) |
+----------+----------+
| 1 | 1 |
+----------+----------+
1 row in set (0.00 sec)
mysql> alter table `test` modify num bit(5);
Query OK, 1 row affected (0.10 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> insert into `test`(num) values (8);
Query OK, 1 row affected (0.00 sec)
mysql> select * from test;
+------------+
| num |
+------------+
| 0x01 |
| 0x08 |
+------------+
2 rows in set (0.00 sec)
mysql> select bin(num),hex(num) from test;
+----------+----------+
| bin(num) | hex(num) |
+----------+----------+
| 1 | 1 |
| 1000 | 8 |
+----------+----------+
2 rows in set (0.00 sec)