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mysql数据类型和用法

Jun 07, 2016 pm 03:01 PM
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欢迎进入Linux社区论坛,与200万技术人员互动交流 >>进入 MySQL支持多种列类型:数值类型、日期/时间类型和字符串(字符)类型。本章首先对这些列类型进行了概述,然后更加详细地描述了各种列的类型,以及列类型存储需求的总结。概述很简单。关于具体列类型

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  MySQL支持多种列类型:数值类型、日期/时间类型和字符串(字符)类型。本章首先对这些列类型进行了概述,然后更加详细地描述了各种列的类型,以及列类型存储需求的总结。概述很简单。关于具体列类型的详细信息应查阅详细的描述,例如指定值时允许使用的格式。

  MySQL支持处理空间数据的扩展名。

  几种列类型描述使用了下述惯例:

  M:表示最大显示宽度。最大有效显示宽度是255.

  M指示最大显示宽度。最大有效显示宽度是255.显示宽度与存储大小或类型包含的值的范围无关。

  D:适用于浮点和定点类型,并表示小数点后面的位数。最大可能的值是30,但不应大于M-2.

  方括号('['和']')表示可选部分。

  如果为一个数值列指定ZEROFILL,MySQL自动为该列添加UNSIGNED属性。

  SERIAL是BIGINT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE的一个别名。

  在整数列定义中,SERIAL DEFAULT VALUE是NOT NULL AUTO_INCREMENT UNIQUE的一个别名。

  BIT[(M)]

  位字段类型。M表示每个值的位数,范围为从1到64.如果M被省略,默认为1.

  TINYINT[(M)] [UNSIGNED] [ZEROFILL]

  很小的整数。带符号的范围是-128到127.无符号的范围是0到255.

  BOOL,BOOLEAN

  是TINYINT(1)的同义词。zero值被视为假。非zero值视为真。

  INT[(M)] [UNSIGNED] [ZEROFILL]

  普通大小的整数。带符号的范围是-2147483648到2147483647.无符号的范围是0到4294967295.

  BIGINT[(M)] [UNSIGNED] [ZEROFILL]

  大整数。带符号的范围是-9223372036854775808到9223372036854775807.无符号的范围是0到18446744073709551615.

  作为SQL标准的扩展,MySQL也支持整数类型TINYINT、MEDIUMINT和BIGINT.下面的表显示了需要的每个整数类型的存储和范围。

  类型

  字节

  最小值

  最大值

  (带符号的/无符号的)

  (带符号的/无符号的)

  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

  CHAR和VARCHAR类型

  CHAR和VARCHAR类型类似,但它们保存和检索的方式不同。它们的最大长度和是否尾部空格被保留等方面也不同。在存储或检索过程中不进行大小写转换。

  CHAR和VARCHAR类型声明的长度表示你想要保存的最大字符数。例如,CHAR(30)可以占用30个字符。

  CHAR列的长度固定为创建表时声明的长度。长度可以为从0到255的任何值。当保存CHAR值时,在它们的右边填充空格以达到指定的长度。当检索到CHAR值时,尾部的空格被删除掉。在存储或检索过程中不进行大小写转换。

  VARCHAR列中的值为可变长字符串。长度可以指定为0到65,535之间的值。(VARCHAR的最大有效长度由最大行大小和使用的字符集确定。整体最大长度是65,532字节)。

  同CHAR对比,VARCHAR值保存时只保存需要的字符数,另加一个字节来记录长度(如果列声明的长度超过255,则使用两个字节)。

  VARCHAR值保存时不进行填充。当值保存和检索时尾部的空格仍保留,符合标准SQL.

  如果分配给CHAR或VARCHAR列的值超过列的最大长度,则对值进行裁剪以使其适合。如果被裁掉的字符不是空格,则会产生一条警告。如果裁剪非空格字符,则会造成错误(而不是警告)并通过使用严格SQL模式禁用值的插入。参见5.3.2节,"SQL服务器模式".

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mysql数据类型和用法

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