mysql数据类型和用法
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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