MySQL INT 含义

Question

我想知道如果我取一个值为 8 的 INT，这是否意味着我只能从 1 到 99999999 或从 1 到 4294967295 UNSIGNED？

Answer 1

文档似乎对此非常清楚：

数值类型属性

MySQL 支持扩展以可选地指定显示 base 关键字后面括号中整数数据类型的宽度 对于类型。例如，INT(4) 指定一个带显示的 INT 四位数的宽度。这个可选的显示宽度可以由 应用程序来显示宽度小于 通过用空格向左填充它们为列指定的宽度。 （那 也就是说，这个宽度存在于与结果集一起返回的元数据中。 是否使用取决于应用程序。）

显示宽度不限制可取值范围 存储在列中。它也不会阻止比列更宽的值 显示宽度无法正确显示。例如，一列 指定为 SMALLINT(3) 的 SMALLINT 范围通常为 -32768 到 32767，三位数允许范围之外的值是 使用三个以上的数字完整显示。

http://dev.mysql.com/doc/refman/5.5/en/numeric-types.html

Answer 2

您必须明确选择无符号，否则默认情况下它是有符号整数，因此您的值也可以是负数。并查看 Tom Squires 提供的链接上的文档。

顺便说一句，看看我发现了什么 -> http://help.scibit.com/mascon/masconMySQL_Field_Types.html

Type
Use for
Size

TINYINT
A very small integer
The signed range is –128 to 127. The unsigned range is 0 to 255.

SMALLINT
A small integer
The signed range is –32768 to 32767. The unsigned range is 0 to 65535

MEDIUMINT
A medium-size integer
The signed range is –8388608 to 8388607. The unsigned range is 0 to 16777215

INT or INTEGER
A normal-size integer
The signed range is –2147483648 to 2147483647. The unsigned range is 0 to 4294967295

BIGINT 
A large integer
The signed range is –9223372036854775808 to 9223372036854775807. The unsigned range is 0 to 18446744073709551615

FLOAT
A small (single-precision) floating-point number. Cannot be unsigned
Ranges are –3.402823466E+38 to –1.175494351E-38, 0 and 1.175494351E-38 to 3.402823466E+38. If the number of Decimals is not set or <= 24 it is a single-precision floating point number

DOUBLE, DOUBLE PRECISION, REAL 
A normal-size (double-precision) floating-point number. Cannot be unsigned 
Ranges are -1.7976931348623157E+308 to -2.2250738585072014E-308, 0 and 2.2250738585072014E-308 to 1.7976931348623157E+308. If the number of Decimals is not set or 25 <= Decimals <= 53 stands for a double-precision floating point number

DECIMAL, NUMERIC 
An unpacked floating-point number. Cannot be unsigned 
Behaves like a CHAR column: “unpacked” means the number is stored as a string, using one character for each digit of the value. The decimal point, and, for negative numbers, the ‘-‘ sign is not counted in Length. If Decimals is 0, values will have no decimal point or fractional part. The maximum range of DECIMAL values is the same as for DOUBLE, but the actual range for a given DECIMAL column may be constrained by the choice of Length and Decimals. If Decimals is left out it’s set to 0. If Length is left out it’s set to 10. Note that in MySQL 3.22 the Length includes the sign and the decimal point 

DATE
A date
The supported range is ‘1000-01-01’ to ‘9999-12-31’. MySQL displays DATE values in ‘YYYY-MM-DD’ format

DATETIME
A date and time combination
The supported range is ‘1000-01-01 00:00:00’ to ‘9999-12-31 23:59:59’. MySQL displays DATETIME values in ‘YYYY-MM-DD HH:MM:SS’ format

TIMESTAMP
A timestamp
The range is ‘1970-01-01 00:00:00’ to sometime in the year 2037. MySQL displays TIMESTAMP values in YYYYMMDDHHMMSS, YYMMDDHHMMSS, YYYYMMDD or YYMMDD format, depending on whether M is 14 (or missing), 12, 8 or 6, but allows you to assign values to TIMESTAMP columns using either strings or numbers. A TIMESTAMP column is useful for recording the date and time of an INSERT or UPDATE operation because it is automatically set to the date and time of the most recent operation if you don’t give it a value yourself

TIME
A time
The range is ‘-838:59:59’ to ‘838:59:59’. MySQL displays TIME values in ‘HH:MM:SS’ format, but allows you to assign values to TIME columns using either strings or numbers

YEAR
A year in 2- or 4- digit formats (default is 4-digit)
The allowable values are 1901 to 2155, and 0000 in the 4 year format and 1970-2069 if you use the 2 digit format (70-69). MySQL displays YEAR values in YYYY format, but allows you to assign values to YEAR columns using either strings or numbers. (The YEAR type is new in MySQL 3.22.)

CHAR
A fixed-length string that is always right-padded with spaces to the specified length when stored
The range of Length is 1 to 255 characters. Trailing spaces are removed when the value is retrieved. CHAR values are sorted and compared in case-insensitive fashion according to the default character set unless the BINARY keyword is given

VARCHAR
A variable-length string. Note: Trailing spaces are removed when the value is stored (this differs from the ANSI SQL specification)
The range of Length is 1 to 255 characters. VARCHAR values are sorted and compared in case-insensitive fashion unless the BINARY keyword is given

TINYBLOB, TINYTEXT
A BLOB or TEXT column with a maximum length of 255 (2^8 - 1) characters 

BLOB, TEXT
A BLOB or TEXT column with a maximum length of 65535 (2^16 - 1) characters

MEDIUMBLOB, MEDIUMTEXT
A BLOB or TEXT column with a maximum length of 16777215 (2^24 - 1) characters 

LONGBLOB, LONGTEXT
A BLOB or TEXT column with a maximum length of 4294967295 (2^32 - 1) characters 

ENUM 
An enumeration 
A string object that can have only one value, chosen from the list of values ‘value1’, ‘value2’, ..., or NULL. An ENUM can have a maximum of 65535 distinct values. 

SET 
A set 
A string object that can have zero or more values, each of which must be chosen from the list of values ‘value1’, ‘value2’, ... A SET can have a maximum of 64 members 

Answer 3

按照documentation、INT(8) 表示您将显示宽度设置为“至少8”，但是：

显示宽度不限制可以存储在列中的值的范围。它也不会阻止正确显示比列显示宽度更宽的值。

Answer 4

看看mysql documentation。它让您了解所有数据类型的细节。无符号最大值为 4294967295