Oracle常用函数:DateDiff() 返回两个日期之间的时间间隔自定义函数

首先在oracle中没有datediff()函数
可以用以下方法在oracle中实现该函数的功能:
1.利用日期间的加减运算
天：
ROUND(TO_NUMBER(END_DATE - START_DATE))
小时：
ROUND(TO_NUMBER(END_DATE - START_DATE) * 24)
分钟：
ROUND(TO_NUMBER(END_DATE - START_DATE) * 24 * 60)
秒：
ROUND(TO_NUMBER(END_DATE - START_DATE) * 24 * 60 * 60)
毫秒：
ROUND(TO_NUMBER(END_DATE - START_DATE) * 24 * 60 * 60 * 60)

2.写函数
Create Or Replace Function CDate(Datechar In Varchar2) Return Date Is  
    ReallyDo Date;   
Begin  
    Select to_date(to_char(to_date(to_char(Datechar), 'YYYY-MM-DD HH24:MI:SS'),   
                           'YYYY-MM-DD'),   
                   'YYYY-MM-DD')   
    Into ReallyDo   
    From Dual;   
    Return(ReallyDo);   
End CDate;   

Create Or Replace Function CDateTime(Datechar In Varchar2) Return Date Is  
    ReallyDo Date;   
Begin  
    Select to_date(to_char(to_date(to_char(Datechar), 'YYYY-MM-DD HH24:MI:SS'),   
                           'YYYY-MM-DD HH24:MI:SS'),   
                   'YYYY-MM-DD HH24:MI:SS')   
    Into ReallyDo   
    From Dual;   
    Return(ReallyDo);   
End CDateTime;   

Create Or Replace Function Datediff   
(   
    Datepart  In Varchar2,   
    StartDate In Varchar2,   
    EndDate   In Varchar2   
) Return Number Is  
    ReallyDo Numeric;   
Begin  
    Select Case Upper(Datepart)   
               When 'YYYY' Then  
                Trunc(Extract(Year From CDate(EndDate)) -   
                      Extract(Year From CDate(StartDate)))   
               When 'M' Then  
                Datediff('YYYY', StartDate, EndDate) * 12 +   
                (Extract(Month From CDate(EndDate)) -   
                 Extract(Month From CDate(StartDate)))   
               When 'D' Then  
                Trunc(CDate(EndDate) - CDate(StartDate))   
               When 'H' Then  
                Datediff('D', StartDate, EndDate) * 24 +   
                (to_Number(to_char(CDateTime(EndDate), 'HH24')) -   
                 to_Number(to_char(CDateTime(StartDate), 'HH24')))   
               When 'N' Then  
                Datediff('D', StartDate, EndDate) * 24 * 60 +   
                (to_Number(to_char(CDateTime(EndDate), 'MI')) -   
                 to_Number(to_char(CDateTime(StartDate), 'MI')))   
               When 'S' Then  
                Datediff('D', StartDate, EndDate) * 24 * 60 * 60 +   
                (to_Number(to_char(CDateTime(EndDate), 'SS')) -   
                 to_Number(to_char(CDateTime(StartDate), 'SS')))   
               Else  
                -29252888   
           End  
    Into ReallyDo   
    From Dual;   
    Return(ReallyDo);   
End Datediff;

 

Oracle常用函数:DateDiff() 返回两个日期之间的时间间隔自定义函数

（当然也有其他方法实现，在ORACLE里日期类型是可以直接进行比较的，最后会给出方法示例）

Create Or Replace Function CDate(Datechar In Varchar2) Return Date Is
    ReallyDo Date;
Begin
    Select to_date(to_char(to_date(to_char(Datechar), 'YYYY-MM-DD HH24:MI:SS'),
                           'YYYY-MM-DD'),
                   'YYYY-MM-DD')
    Into ReallyDo
    From Dual;
    Return(ReallyDo);
End CDate;



Create Or Replace Function CDateTime(Datechar In Varchar2) Return Date Is
    ReallyDo Date;
Begin
    Select to_date(to_char(to_date(to_char(Datechar), 'YYYY-MM-DD HH24:MI:SS'),
                           'YYYY-MM-DD HH24:MI:SS'),
                   'YYYY-MM-DD HH24:MI:SS')
    Into ReallyDo
    From Dual;
    Return(ReallyDo);
End CDateTime;



Create Or Replace Function Datediff
(
    Datepart  In Varchar2,
    StartDate In Varchar2,
    EndDate   In Varchar2
) Return Number Is
    ReallyDo Numeric;
Begin
    Select Case Upper(Datepart)
               When 'YYYY' Then
                Trunc(Extract(Year From CDate(EndDate)) -
                      Extract(Year From CDate(StartDate)))
               When 'M' Then
                Datediff('YYYY', StartDate, EndDate) * 12 +
                (Extract(Month From CDate(EndDate)) -
                 Extract(Month From CDate(StartDate)))
               When 'D' Then
                Trunc(CDate(EndDate) - CDate(StartDate))
               When 'H' Then
                Datediff('D', StartDate, EndDate) * 24 +
                (to_Number(to_char(CDateTime(EndDate), 'HH24')) -
                 to_Number(to_char(CDateTime(StartDate), 'HH24')))
               When 'N' Then
                Datediff('D', StartDate, EndDate) * 24 * 60 +
                (to_Number(to_char(CDateTime(EndDate), 'MI')) -
                 to_Number(to_char(CDateTime(StartDate), 'MI')))
               When 'S' Then
                Datediff('D', StartDate, EndDate) * 24 * 60 * 60 +
                (to_Number(to_char(CDateTime(EndDate), 'SS')) -
                 to_Number(to_char(CDateTime(StartDate), 'SS')))
               Else
                -29252888
           End
    Into ReallyDo
    From Dual;
    Return(ReallyDo);
End Datediff;

 

 当然也有其他方法实现

 在ORACLE里日期类型是可以直接进行比较的。举个例子：

SQL> SELECT to_date('2011-10-05', 'yyyy-mm-dd') - to_date('2011-10-07', 'yyyy-mm-dd') FROM dual ;

TO_DATE('2011-10-05','YYYY-MM-DD')-TO_DATE('2011-10-07','YYYY-MM-DD')
---------------------------------------------------------------------
                                                                   -2

这说明2011-10-05要比7号早2天。

SQL> SELECT to_date('2011-10-07 14:23:24' , 'yyyy-mm-dd hh24:mi:ss') + 1/24 FROM dual ;

TO_DATE('2011-10-07
-------------------
2011-10-07 15:23:24

SQL>

这是说明在某一时间上加一小时，1是代表一天，1/24就是一小时，同理1/24/60就是一分钟