SQL CAST, CONVERT 比较

本文转自：http://www.cnblogs.com/denylau/archive/2010/12/01/1893371.html

if (@StartTime > @EndTime)
    Set @EndTime = cast (convert (char , @ScheduleDate + 1 , 101)+' '+convert (char , @EndTime, 108) as datetime )    
Else
    Set @EndTime = cast (convert (char , @ScheduleDate  , 101)+' '+convert (char , @EndTime, 108) as datetime )
    
Set @StartTime = cast (convert (char , @ScheduleDate , 101)+' '+convert (char , @StartTime, 108) as datetime )

这条语句中的Convert,Cast 的意思,作用

Convert (data_type[,length],expression[,style])

这个转换函数一般在时间类型和字符串类型转换的时候才用到.

style格式在转换时间时候的格式如下:

Style(2位表示年份)    |   Style(4位表示年份)    |    输入输出格式                                    
------------------------------------------------------------------------------------------------------------
0                                | 100                            |    mon dd yyyy hh:miAM(或PM)              
------------------------------------------------------------------------------------------------------------
1                                |   101    美国                 |    mm/dd/yy                                       
------------------------------------------------------------------------------------------------------------
2                                |   102     ANSI                |    yy-mm-dd                                         
------------------------------------------------------------------------------------------------------------
3                                |   103     英法                 |    dd/mm/yy                                       
------------------------------------------------------------------------------------------------------------
4                                |   104     德国                 |    dd.mm.yy                                        
------------------------------------------------------------------------------------------------------------
5                                |   105     意大利              |    dd-mm-yy                                         
------------------------------------------------------------------------------------------------------------
6                                |   106                             |    dd mon yy                                        
------------------------------------------------------------------------------------------------------------
7                                |   107                             |    mon dd,yy                                        
------------------------------------------------------------------------------------------------------------
8                                |   108                             |    hh:mm:ss                                         
------------------------------------------------------------------------------------------------------------
9                                |   109                             |    mon dd yyyy hh:mi:ss:mmmmAM(或PM)
------------------------------------------------------------------------------------------------------------
10                              |   110     美国                  |    mm-dd-yy                                         
------------------------------------------------------------------------------------------------------------
11                              |   111     日本                  |    yy/mm/dd                                        
------------------------------------------------------------------------------------------------------------
12                              |   112     ISO                   |    yymmdd                                           
------------------------------------------------------------------------------------------------------------
13                              |   113      欧洲默认值      |    dd mon yyyy hh:mi:ss:mmm(24小时制)  
------------------------------------------------------------------------------------------------------------
14                              |   114                             |    hh:mi:ss:mmm(24小时制)                    
------------------------------------------------------------------------------------------------------------
20                              |   120      ODBC 规范      |     yyyy-mm-dd hh:mi:ss(24小时制)          
------------------------------------------------------------------------------------------------------------
21                              |    121                            |     yyyy-mm-dd hh:mi:ss:mmm(24小时制)

Cast(Expression as data_type) : 将某种数据类型的数据显示转换为另外一种类型.

select top 1 starttime from itemtransaction
select top 1 convert (char ,starttime+1,102) from itemtransaction
select top 1 Convert (char ,starttime,108) from itemtransaction

select top 1 cast (( convert (char ,starttime+1,102)+Convert (char ,starttime,108)) as datetime ) from itemtransaction 
显示结果: