在informix中有如下几种对字符串操作的类型： char(character),varchar,nchar,nvarchar,lvarchar,text 在ORACLE中有如下几种对字符串操作的类型： char(character),varchar(varchar2),nchar,nvarchar2,long,long raw及LOB类型

一、基本概念： 1、字符存储单位 2、char:定长的字符串类型 3、varchar：描述变长字符串

二、INFORMIX ORACLES数据类型对应长度及比较 informix Oracle 范围 默认长度 作为数据存储 变量 char 1~32767 1 1~2000 1~32767 varchar 1~255 1 1~4000 1~

三、字符比较： 1、char和varchar 2、char和nchar，varchar和nvarchar

四、oracle里的数据类型: 1、char,character,varchar,varchar2,nchar,nvarchar2的共同特点： 当插入空字符串时，则都会被转变为null

五、informix里的字符: 1、lvarchar在9.4版本之后才可以用带指定长度的方式，如lvarchar(3000)，不带长度则默认是2048字节，最大长度是32,739字节。 所以对于9.4之前的版本，不能用带长度的表达式，数据库会报语法错误。

六、oracle和informix表的限制 1、在informix的一个表中对以上字符串类型定义的总长度不能超过32767(不包括对大字段处理的text类型) 但是遇到varchar与nvarchar会再减1(为该列设置索引会留一位)，而遇到lvarchar则需要减3。 2、oracle限制的每个表的列的总数不能超过1000(此处没有测试),然后每个列的长度由其数据类型决定。 每个索引的最大列数 32

七、行迁移与行链接 当一行的数据过长而不能插入一个单个数据块中时，可能发生两种事情：行链接(row chaining)或行迁移(row migration)。

八、ORACLE－在设计数据库时如何选择正确的数据类型

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