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mysql基础:列类型--整型

 

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

说明:

·         M

表示最大显示宽度。最大有效显示宽度是255。

·         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。

注:上面NOT NULL是不可为空,AUTO_INCREMENT是递增,指定起始值为1用AUTO_INCREMENT=1语句,不指定默认也为1。

UNIQE是不可重复的意思,取值不能与已经存在的数据重复。

 

整型数据

·         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。

在将来,将根据标准SQL引入完全布尔类型的处理。

·         SMALLINT[(M)] [UNSIGNED] [ZEROFILL]

小的整数。带符号的范围是-32768到32767。无符号的范围是0到65535。

·         MEDIUMINT[(M)] [UNSIGNED] [ZEROFILL]

中等大小的整数。带符号的范围是-8388608到8388607。无符号的范围是0到16777215。

·         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。

·         INTEGER[(M)] [UNSIGNED] [ZEROFILL]

这是INT的同义词。

·         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。

    ·        

 FLOAT[(M,D)] [UNSIGNED] [ZEROFILL]

 

小(单精度)浮点数。允许的值是-3.402823466E+38到-1.175494351E-38、0和1.175494351E-38到3.402823466E+38。这些是理论限制,基于IEEE标准。实际的范围根据硬件或操作系统的不同可能稍微小些。

M是小数纵位数,D是小数点后面的位数。如果M和D被省略,根据硬件允许的限制来保存值。单精度浮点数精确到大约7位小数位。

如果指定UNSIGNED,不允许负值。

·        

 DOUBLE[(M,D)] [UNSIGNED] [ZEROFILL]

 

普通大小(双精度)浮点数。允许的值是-1.7976931348623157E+308到-2.2250738585072014E-308、0和2.2250738585072014E-308到 1.7976931348623157E+308。这些是理论限制,基于IEEE标准。实际的范围根据硬件或操作系统的不同可能稍微小些。

M是小数总位数,D是小数点后面的位数。如果M和D被省略,根据硬件允许的限制来保存值。双精度浮点数精确到大约15位小数位。

如果指定UNSIGNED,不允许负值。

·         

DOUBLE PRECISION[(M,D)] [UNSIGNED] [ZEROFILL], REAL[(M,D)] [UNSIGNED] [ZEROFILL]

 

为DOUBLE的同义词。除了:如果SQL服务器模式包括REAL_AS_FLOAT选项,REAL是FLOAT的同义词而不是DOUBLE的同义词。

·         

FLOAT(p) [UNSIGNED] [ZEROFILL]

 

浮点数。p表示精度(以位数表示),但MySQL只使用该值来确定是否结果列的数据类型为FLOAT或DOUBLE。如果p为从0到24,数据类型变为没有M或D值的FLOAT。如果p为从25到53,数据类型变为没有M或D值的DOUBLE。结果列范围与本节前面描述的单精度FLOAT或双精度DOUBLE数据类型相同。

FLOAT(p)语法与ODBC兼容。

·        

 DECIMAL[(M[,D])] [UNSIGNED] [ZEROFILL]

 

压缩的“严格”定点数。M是小数位数(精度)的总数,D是小数点(标度)后面的位数。小数点和(负数)的‘-’符号不包括在M中。如果D是0,则值没有小数点或分数部分。DECIMAL整数最大位数(M)为65。支持的十进制数的最大位数(D)是30。如果D被省略, 默认是0。如果M被省略, 默认是10。

如果指定UNSIGNED,不允许负值。

所有DECIMAL列的基本计算(+,-,*,/)用65位精度完成。

·         DEC[(M[,D])] [UNSIGNED] [ZEROFILL], NUMERIC[(M[,D])] [UNSIGNED] [ZEROFILL], FIXED[(M[,D])] [UNSIGNED] [ZEROFILL]

 

是DECIMAL的同义词。FIXED同义词适用于与其它服务器的兼容性。

 

mysql基础:列类型--整型_MySQL

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