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）

Sql代码  

1. Create Or Replace Function CDate(Datechar In Varchar2) Return Date Is  
2.     ReallyDo Date;  
3. Begin  
4.     Select to_date(to_char(to_date(to_char(Datechar), \'YYYY-MM-DD HH24:MI:SS\'),  
5.                            \'YYYY-MM-DD\'),  
6.                    \'YYYY-MM-DD\')  
7.     Into ReallyDo  
8.     From Dual;  
9.     Return(ReallyDo);  
10. End CDate;  
11.   
12.    
13.   
14. Create Or Replace Function CDateTime(Datechar In Varchar2) Return Date Is  
15.     ReallyDo Date;  
16. Begin  
17.     Select to_date(to_char(to_date(to_char(Datechar), \'YYYY-MM-DD HH24:MI:SS\'),  
18.                            \'YYYY-MM-DD HH24:MI:SS\'),  
19.                    \'YYYY-MM-DD HH24:MI:SS\')  
20.     Into ReallyDo  
21.     From Dual;  
22.     Return(ReallyDo);  
23. End CDateTime;  
24.   
25.    
26.   
27. Create Or Replace Function Datediff  
28. (  
29.     Datepart  In Varchar2,  
30.     StartDate In Varchar2,  
31.     EndDate   In Varchar2  
32. ) Return Number Is  
33.     ReallyDo Numeric;  
34. Begin  
35.     Select Case Upper(Datepart)  
36.                When \'YYYY\' Then  
37.                 Trunc(Extract(Year From CDate(EndDate)) -  
38.                       Extract(Year From CDate(StartDate)))  
39.                When \'M\' Then  
40.                 Datediff(\'YYYY\', StartDate, EndDate) * 12 +  
41.                 (Extract(Month From CDate(EndDate)) -  
42.                  Extract(Month From CDate(StartDate)))  
43.                When \'D\' Then  
44.                 Trunc(CDate(EndDate) - CDate(StartDate))  
45.                When \'H\' Then  
46.                 Datediff(\'D\', StartDate, EndDate) * 24 +  
47.                 (to_Number(to_char(CDateTime(EndDate), \'HH24\')) -  
48.                  to_Number(to_char(CDateTime(StartDate), \'HH24\')))  
49.                When \'N\' Then  
50.                 Datediff(\'D\', StartDate, EndDate) * 24 * 60 +  
51.                 (to_Number(to_char(CDateTime(EndDate), \'MI\')) -  
52.                  to_Number(to_char(CDateTime(StartDate), \'MI\')))  
53.                When \'S\' Then  
54.                 Datediff(\'D\', StartDate, EndDate) * 24 * 60 * 60 +  
55.                 (to_Number(to_char(CDateTime(EndDate), \'SS\')) -  
56.                  to_Number(to_char(CDateTime(StartDate), \'SS\')))  
57.                Else  
58.                 -29252888  
59.            End  
60.     Into ReallyDo  
61.     From Dual;  
62.     Return(ReallyDo);  
63. 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