set nocount on
declare @logicalfilename sysname,
        @maxminutes int,
        @newsize int
use     tablename            
-- 要操作的数据库名
select  @logicalfilename = 'tablename_log', 
-- 日志文件名
@maxminutes = 10,              
-- limit on time allowed to wrap log.
        @newsize = 1                 
-- 你想设定的日志文件的大小(m)
-- setup / initialize
declare @originalsize int
select @originalsize = size
  from sysfiles
  where name = @logicalfilename
select 'original size of ' + db_name() + ' log is ' +
        convert(varchar(30),@originalsize) + ' 8k pages or ' +
        convert(varchar(30),(@originalsize*8/1024)) + 'mb'
  from sysfiles
  where name = @logicalfilename
create table dummytrans
  (dummycolumn char (8000) not null)
declare @counter   int,
        @starttime datetime,
        @trunclog  varchar(255)
select  @starttime = getdate(),
        @trunclog = 'backup log '
 + db_name() + ' with truncate_only'

dbcc shrinkfile (@logicalfilename, @newsize)
exec (@trunclog)
-- wrap the log if necessary.
while     @maxminutes > datediff
(mi, @starttime, getdate()) -- time has not expired
      and @originalsize =
(select size from sysfiles where name = @logicalfilename) 
      and (@originalsize * 8 /1024) > @newsize 
  begin -- outer loop.
    select @counter = 0
    while  ((@counter < @originalsize / 16) and (@counter < 50000))
      begin -- update
        insert dummytrans values ('fill log') 
        delete dummytrans
        select @counter = @counter + 1
      end  
    exec (@trunclog) 
  end  
select 'final size of ' + db_name() + ' log is ' +
        convert(varchar(30),size) + ' 8k pages or ' +
        convert(varchar(30),(size*8/1024)) + 'mb'
  from sysfiles
  where name = @logicalfilename
drop table dummytrans
set nocount off