oracle 中的round()函数、null值,rownum

round()函数:四舍五入函数

传回一个数值,该数值按照指定精度进行四舍五入运算的结果。

语法:round(number[,decimals])

Number:待处理的函数

Decimals:精度,默认为0;

Select round(123.456,0) as a,round(123.456,1) as b,round(123.456,-1) as c from dual;

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null值:

NULL值就是没有值或者缺值。允许NULL值的列也允许在插入行时不给出该列的值。不允许NULL值的列不接受该列没有值的行,换句话说,在插入或更新行时,该列必须有值。

每个表列或者是NULL值,或者是NOT NULL列,这种状态在创建时有表的定义规定,如:

CREATE TABLE Orders

(

  order_num  INTEGER  NOT NULL,

  order_date DATETIME NOT NULL,

  order_id   CHAR(10) NOT NULL

);

以上语句创建了一个表,改表有3个字段,每个字段被关键字NOT NULL限定,故在插入没有值的列,将会返回错误,且插入失败。

rownum:

rownum只能用于<,如果要用>,可以用一下两者方法实现:

用ROW_NUMBER() OVER():

select areaid from
( select areaid, ROW_NUMBER() OVER( order by areaid ) t
from cumenu ) k
where t > 5;

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" alt="" />

实例化:

select areaid from
( select areaid, rownum r
from cumenu )
where r > 5;

aaarticlea/png;base64,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" alt="" />

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本系列为最近一段时间学习oracle的学习笔记,记录于此作为自身回顾,其中有的来的网络,有的来的书籍,但时间已久,记不清哪些是引用,如是转载但没标注出,特意致歉。

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