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PL/SQL数据类型及操作符

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Jun 07, 2016 pm 06:04 PM

PL/SQL数据类型及操作符

标量(scalar)数据类型

　　标量(scalar)数据类型没有内部组件，他们大致可分为以下四类：

　　　. number
　　　. character
　　　. date/time
　　　. boolean

　　表1显示了数字数据类型；表2显示了字符数据类型；表3显示了日期和布尔数据类型。

　　表1 Scalar Types:Numeric

　　NUMBER 数字型能存放整数值和实数值，并且可以定义精度和取值范围
　　BINARY_INTEGER 数字型可存储带符号整数，为整数计算优化性能
　　DEC 数字型 NUMBER的子类型，小数
　　DOUBLE PRECISION 数字型 NUMBER的子类型，高精度实数
　　INTEGER 数字型 NUMBER的子类型，整数
　　INT 数字型 NUMBER的子类型，整数
　　NUMERIC 数字型 NUMBER的子类型，与NUMBER等价
　　REAL 数字型 NUMBER的子类型，与NUMBER等价
　　SMALLINT 数字型 NUMBER的子类型，取值范围比INTEGER小
　　VARCHAR2 字符型存放可变长字符串，有最大长度

　　表2 字符数据类型

　　CHAR 字符型定长字符串
　　LONG 字符型变长字符串，最大长度可达32,767
　　DATE 日期型以数据库相同的格式存放日期值
　　BOOLEAN 布尔型 TRUE OR FALSE
　　ROWID ROWID 存放数据库的行号

　　表3 DATE和BOOLEAN

　　LOB数据类型

　　LOB(大对象,Large object) 数据类型用于存储类似图像，声音这样的大型数据对象，LOB数据对象可以是二进制数据也可以是字符数据，其最大长度不超过4G。LOB数据类型支持任意访问方式，LONG只支持顺序访问方式。LOB存储在一个单独的位置上，同时一个"LOB定位符"(LOB locator)存储在原始的表中，该定位符是一个指向实际数据的指针。在PL/SQL中操作LOB数据对象使用提供的包DBMS_LOB.LOB数据类型可分为以下四类：

　　. BFILE
　　. BLOB
　　. CLOB
　　. NCLOB

　　操作符

　　与其他程序语言相同，PL/SQL有一系列操作符。操作符分为下面几类：

　　. 算术操作符

　　. 关系操作符

　　. 比较操作符

　　. 逻辑操作符

　　算术操作符如表4所示

　　关系操作符主要用于条件判断语句或用于where子串中，关系操作符检查条件和结果是否为true或false,表5是PL/SQL中的关系操作符

　　表6 显示的是比较操作符

　　表7.8显示的是逻辑操作符

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