oralce, DB2 , sql server , mysql各数据库字段总结

<p style="text-align: center;"><strong><span style="font-size: large;"><span style="color: #ff0000;">oracle</span></span></strong></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>数据类型</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>取值范围</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>描述</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>备注</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Char(n)</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>n=1 to 2000字节</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>存储固定长度的字符串。默认长度为1。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>&nbsp;</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Varchar2(n)</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>n=1 to 4000字节</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>可变长的字符串，具体定义时指明最大长度n，<br />这种数据类型可以放数字、字母以及ASCII码字符集(或者EBCDIC等数据库系统接受的字符集标准)中的所有符号。<br />如果数据长度没有达到最大值n，Oracle 会根据数据大小自动调节字段长度，<br />如果你的数据前后有空格，Oracle 8会自动将其删去。VARCHAR2是最常用的数据类型。<br />可做索引的最大长度3209。Varchar2类型的字段长度可以达到4000字节，Varchar2类型的变量长度可以达到32676字节。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>节省表空间：一个空的varchar2(2000)字段和一个空的varchar2(2)字段所占用的空间是一样的。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Nchar(n)</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>n=1 to 2000字节</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Unicode数据类型，只能存储utf-16和utf-8的数据。存储固定长度的字符串。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>&nbsp;</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Nvarchar2(n)</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>n=1 to 4000字节</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Unicode数据类型，只能存储utf-16和utf-8的数据。存储变长字符串。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>&nbsp;</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Long</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>最大2G</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>可变长字符列，最大长度限制是2GB，用于不需要作字符串搜索的长串数据，如果要进行字符搜索就要用varchar2类型。<br />long是一种较老的数据类型，将来会逐渐被BLOB、CLOB、NCLOB等大的对象数据类型所取代。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>在不同系统间移动需要进行转换。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Clob</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>最大4G</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>存储单字节字符型数据。适用于存储超长文本。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>&nbsp;</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Nclob</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>最大4G</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>存储多字节国家字符型数据。适用于存储超长文本。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>&nbsp;</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Blob</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>最大4G</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>存储二进制数据。适用于存储图像、视频、音频等。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>&nbsp;</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Bfile</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>最大长度是4GB</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>在数据库外部保存的大型二进制对象文件，最大长度是4GB。这种外部的LOB类型，通过数据库记录变化情况，但是数据的具体保存是在数据库外部进行的。</strong></span></p>
<p class="MsoNormal"><span style="font-size: small;"><strong>Oracle 可以读取、查询BFILE，但是不能写入，不参与事务。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>&nbsp;</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Number(m,n)</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>m=1 to 38<br />n=-84 to 127</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>存储整数或浮点数。可变长的数值列，允许0、正值及负值，m是所有有效数字的位数，n是小数点以后的位数。<br />如：number(5,2)，则这个字段的最大值是99,999，如果数值超出了位数限制就会被截取多余的位数。<br />如：number(5,2)，但在一行数据中的这个字段输入575.316，则真正保存到字段中的数值是575.32。<br />如：number(3,0)，输入575.316，真正保存的数据是575。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>&nbsp;</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Date</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>&nbsp;</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>数据类型用来存储日期和时间格式的数据。默认格式：DD-MON-YYYY。从公元前4712年1月1日到公元4712年12月31日的所有合法日期</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>&nbsp;</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Row(n)</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>n=1 to 2000</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>可变长二进制数据，在具体定义字段的时候必须指明最大长度n，Oracle 用这种格式来保存较小的图形文件或带格式的文本文件，如Miceosoft Word文档。<br />raw是一种较老的数据类型，将来会逐渐被BLOB、CLOB、NCLOB等大的对象数据类型所取代。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>&nbsp;</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>LongRow</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>最大长度是2GB。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>可变长二进制数据，最大长度是2GB。Oracle 用这种格式来保存较大的图形文件或带格式的文本文件，如Miceosoft Word文档，以及音频、视频等非文本文件。<br />在同一张表中不能同时有long类型和long raw类型，long raw也是一种较老的数据类型，将来会逐渐被BLOB、CLOB、NCLOB等大的对象数据类型所取代。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>&nbsp;</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>Rowid</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>&nbsp;</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>数据类型是ORACLE数据表中的一个伪列，它是数据表中每行数据内在的唯一的标识。</strong></span></p>
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<p class="MsoNormal"><span style="font-size: small;"><strong>&nbsp;</strong></span></p>
<p class="MsoNormal"><span style="font-size: small;"><strong><br /></strong></span></p>
<p class="MsoNormal"><span style="font-size: small;"><strong><br /></strong></span></p>
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<p><span style="font-size: small;">注：</span></p>
<p><span style="font-size: small;">1. Number的数据声明如下： <br />表示&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 作用&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 说明 <br />Number(p, s)&nbsp; &nbsp; &nbsp; &nbsp; 声明一个定点数&nbsp; &nbsp; &nbsp; &nbsp; p(precision)为精度，s(scale)表示小数点右边的数字个 数，精度最大值为38，scale的取值范围为-84到127 <br />Number(p)&nbsp; &nbsp; &nbsp; &nbsp; 声明一个整数&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 相当于Number(p, 0) <br />Number&nbsp; &nbsp; &nbsp; &nbsp; 声明一个浮点数&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 其精度为38，要注意的是scale的值没有应用，也就是说scale的指不能简单的理解为0，或者其他的数。 <br /><br />定点数的精度(p)和刻度(s)遵循以下规则： <br />&nbsp; &nbsp; &nbsp; &nbsp; 当一个数的整数部分的长度 &gt; p-s 时，Oracle就会报错 <br />&nbsp; &nbsp; &nbsp; &nbsp; 当一个数的小数部分的长度 &gt; s 时，Oracle就会舍入。 <br />&nbsp; &nbsp; &nbsp; &nbsp; 当s(scale)为负数时，Oracle就对小数点左边的s个数字进行舍入。 <br />&nbsp; &nbsp; &nbsp; &nbsp; 当s &gt; p 时, p表示小数点后第s位向左最多可以有多少位数字，如果大于p则Oracle报错，小数点后s位向右的数字被舍入 </span></p>
<p><span style="font-size: small;">2．Char、Varchar、Varchar2区别&nbsp; </span></p>
<p><span style="font-size: small;">&nbsp;&nbsp;①.CHAR的长度是固定的，而VARCHAR2的长度是可以变化的， 比如，存储字符串&ldquo;abc"，对于CHAR (20)，表示你存储的字符将占20个字节(包括17个空字符)，而同样的VARCHAR2 (20)则只占用3个字节的长度，20只是最大值，当你存储的字符小于20时，按实际长度存储。&nbsp;<br />&nbsp; ②CHAR的效率比VARCHAR2的效率稍高。&nbsp;<br />&nbsp; ③目前VARCHAR是VARCHAR2的同义词。工业标准的VARCHAR类型可以存储空字符串，但是oracle不这样做，尽管它保留以后这样做的权利。Oracle自己开发了一个数据类型VARCHAR2，这个类型不是一个标准的VARCHAR，它将在数据库中varchar列可以存储空字符串的特性改为存储NULL值。如果你想有向后兼容的能力，Oracle建议使用VARCHAR2而不是VARCHAR。 <br />&nbsp; 何时该用CHAR，何时该用varchar2？ <br />&nbsp; CHAR与VARCHAR2是一对矛盾的统一体，两者是互补的关系. <br />&nbsp; VARCHAR2比CHAR节省空间，在效率上比CHAR会稍微差一些，即要想获得效率，就必须牺牲一定的空间，这也就是我们在数据库设计上常说的&lsquo;以空间换效率&rsquo;。 <br />&nbsp; VARCHAR2虽然比CHAR节省空间，但是如果一个VARCHAR2列经常被修改，而且每次被修改的数据的长度不同，这会引起&lsquo;行迁移&rsquo;(Row Migration)现象，而这造成多余的I/O，是数据库设计和调整中要尽力避免的，在这种情况下用CHAR代替VARCHAR2会更好一些。</span></p>
<p><span style="font-size: small;">&nbsp;&nbsp; ④varchar 是 ANSI 标准<br />&nbsp;&nbsp; varchar2 是 oracle 标准<br />&nbsp;&nbsp; 实际上本质目前是一样的，可以看做oracle搞出来的，oracle说：<br />&nbsp;&nbsp; ANSI标准可能随着 SQL-92 / SQl-99/ SQL -NNN&nbsp;&nbsp;等发生变化<br />&nbsp;&nbsp; 但是oracle保证varchar2 永远兼容&hellip;&hellip;<br /></span></p>
<p class="MsoNormal" style="text-align: center;" align="center"><strong><span style="font-size: 14pt; color: red; mso-bidi-font-size: 12.0pt;" lang="EN-US">Sql sever</span></strong></p>
<p class="MsoNormal" style="text-align: center;" align="center"><strong><span style="font-size: 14pt; color: red; mso-bidi-font-size: 12.0pt;" lang="EN-US">&nbsp;</span></strong></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><strong><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-size: 12.0pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型 </span></strong></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><strong><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-size: 12.0pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">类型 </span></strong></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><strong><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-size: 12.0pt; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">描<span lang="EN-US"> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span>述 </span></strong></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">bit </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">整型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">bit </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型是整型，其值只能是<span lang="EN-US">0</span>、<span lang="EN-US">1</span>或空值。这种数据类型用于存储只有两种可能值的数据，如<span lang="EN-US">Yes </span>或<span lang="EN-US">No</span>、<span lang="EN-US">True </span>或<span lang="EN-US">Fa lse </span>、<span lang="EN-US">On </span>或<span lang="EN-US">Off </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">int </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">整型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">int </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型可以存储从<span lang="EN-US">- 2³¹(-2147483648)</span>到<span lang="EN-US">2³¹ (2147483 647)</span>之间的整数。存储到数据库的几乎所有数值型的数据都可以用这种数据类型。这种数据类型在数据库里占用<span lang="EN-US">4</span>个字节<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">smallint </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">整型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">smallint </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型可以存储从<span lang="EN-US">- 2¹⁵(-32768)</span>到<span lang="EN-US">2¹⁵(32767)</span>之间的整数。这种数据类型对存储一些常限定在特定范围内的数值型数据非常有用。这种数据类型在数据库里占用<span lang="EN-US">2 </span>字节空间<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">tinyint </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">整型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">tinyint </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型能存储从<span lang="EN-US">0</span>到<span lang="EN-US">255 </span>之间的整数。它在你只打算存储有限数目的数值时很有用。 这种数据类型在数据库中占用<span lang="EN-US">1 </span>个字节<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">numeric</span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">精确数值型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">numeric</span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型与<span lang="EN-US">decimal </span>型相同<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">decimal </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">精确数值型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">decimal </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型能用来存储从<span lang="EN-US">-10³⁸-1</span>到<span lang="EN-US">10³⁸-1</span>的固定精度和范围的数值型数据。使用这种数据类型时，必须指定范围和精度。 范围是小数点左右所能存储的数字的总位数。精度是小数点右边存储的数字的位数<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">money </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">货币型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">money </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型用来表示钱和货币值。这种数据类型能存储从<span lang="EN-US">-9220</span>亿到<span lang="EN-US">9220 </span>亿之间的数据，精确到货币单位的万分之一<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">smallmoney </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">货币型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">smallmoney </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型用来表示钱和货币值。这种数据类型能存储从<span lang="EN-US">-214748.3648 </span>到<span lang="EN-US">214748.3647 </span>之间的数据，精确到货币单位的万分之一<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">float </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">近似数值型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">float </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型是一种近似数值类型，供浮点数使用。说浮点数是近似的，是因为在其范围内不是所有的数都能精确表示。浮点数可以是从<span lang="EN-US">-1.79E+308</span>到<span lang="EN-US">1.79E+308 </span>之间的任意数<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">real </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">近似数值型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">real </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型像浮点数一样，是近似数值类型。它可以表示数值在<span lang="EN-US">-3.40E+38</span>到<span lang="EN-US">3.40E+38</span>之间的浮点数<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">datetime </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">日期时间型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">datetime</span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型用来表示日期和时间。这种数据类型存储从<span lang="EN-US">1753</span>年<span lang="EN-US">1</span>月<span lang="EN-US">1</span>日到<span lang="EN-US">9999</span>年<span lang="EN-US">12</span>月<span lang="EN-US">3 1</span>日间所有的日期和时间数据， 精确到三百分之一秒或<span lang="EN-US">3.33</span>毫秒<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">Smalldatetime </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">日期时间型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">smalldatetime </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型用来表示从<span lang="EN-US">1900</span>年<span lang="EN-US">1</span>月<span lang="EN-US">1</span>日到<span lang="EN-US">2079</span>年<span lang="EN-US">6</span>月<span lang="EN-US">6</span>日间的日期和时间，精确到一分钟<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">cursor </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">特殊数据型<span lang="EN-US"> </span></span></p>
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<td style="padding: 0.75pt;">
<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">cursor </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型是一种特殊的数据类型，它包含一个对游标的引用。这种数据类型用在存储过程中，而且创建表时不能用<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">timestamp </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">特殊数据型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">timestamp </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型是一种特殊的数据类型，用来创建一个数据库范围内的唯一数码。 一个表中只能有一个<span lang="EN-US">timestamp</span>列。每次插入或修改一行时，<span lang="EN-US">timestamp</span>列的值都会改变。尽管它的名字中有<span lang="EN-US">&ldquo;time&rdquo;</span>， 但<span lang="EN-US">timestamp</span>列不是人们可识别的日期。在一个数据库里，<span lang="EN-US">timestamp</span>值是唯一的<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">Uniqueidentifier </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">特殊数据型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">Uniqueidentifier</span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型用来存储一个全局唯一标识符，即<span lang="EN-US">GUID</span>。<span lang="EN-US">GUID</span>确实是全局唯一的。这个数几乎没有机会在另一个系统中被重建。可以使用<span lang="EN-US">NEWID </span>函数或转换一个字符串为唯一标识符来初始化具有唯一标识符的列<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">char </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">字符型<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">char</span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型用来存储指定长度的定长非统一编码型的数据。当定义一列为此类型时，你必须指定列长。当你总能知道要存储的数据的长度时，此数据类型很有用。例如，当你按邮政编码加<span lang="EN-US">4</span>个字符格式来存储数据时，你知道总要用到<span lang="EN-US">10</span>个字符。此数据类型的列宽最大为<span lang="EN-US">8000 </span>个字符<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">varchar </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">字符型<span lang="EN-US"> </span></span></p>
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<td style="padding: 0.75pt;">
<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">varchar</span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型，同<span lang="EN-US">char</span>类型一样，用来存储非统一编码型字符数据。与<span lang="EN-US">char </span>型不一样，此数据类型为变长。当定义一列为该数据类型时，你要指定该列的最大长度。 它与<span lang="EN-US">char</span>数据类型最大的区别是，存储的长度不是列长，而是数据的长度<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">text </span></p>
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<td style="padding: 0.75pt;">
<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">字符型<span lang="EN-US"> </span></span></p>
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<td style="padding: 0.75pt;">
<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">text </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型用来存储大量的非统一编码型字符数据。这种数据类型最多可以有<span lang="EN-US">2³¹-1</span>或<span lang="EN-US">20</span>亿个字符<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">nchar </span></p>
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<td style="padding: 0.75pt;">
<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">统一编码字符型<span lang="EN-US"> </span></span></p>
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<td style="padding: 0.75pt;">
<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">nchar </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型用来存储定长统一编码字符型数据。统一编码用双字节结构来存储每个字符，而不是用单字节<span lang="EN-US">(</span>普通文本中的情况<span lang="EN-US">)</span>。它允许大量的扩展字符。此数据类型能存储<span lang="EN-US">4000</span>种字符，使用的字节空间上增加了一倍<span lang="EN-US"> </span></span></p>
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<td style="padding: 0.75pt;">
<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">nvarchar </span></p>
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<td style="padding: 0.75pt;">
<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">统一编码字符型<span lang="EN-US"> </span></span></p>
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<td style="padding: 0.75pt;">
<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">nvarchar </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型用作变长的统一编码字符型数据。此数据类型能存储<span lang="EN-US">4000</span>种字符，使用的字节空间增加了一倍<span lang="EN-US"> </span></span></p>
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<tr style="mso-yfti-irow: 21;">
<td style="padding: 0.75pt;">
<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">ntext </span></p>
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<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">统一编码字符型<span lang="EN-US"> </span></span></p>
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<td style="padding: 0.75pt;">
<p class="MsoNormal" style="text-align: center; mso-pagination: widow-orphan;" align="center"><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;" lang="EN-US">ntext </span><span style="font-size: 9pt; font-family: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 0pt;">数据类型用来存储大量的统一编码字符型数据。这种数据类型能存储<span lang="EN-US">2³⁰ -1</span>或将近<span lang="EN-US">10</span>亿个字符，且使用的字节空间增加了一倍<span lang="EN-US"> </span></span></p>
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<p class="MsoNormal" style="text-align: center; mso-