--清除日志：
DECLARE @LogicalFileName sysname,
        @MaxMinutes INT,
        @NewSize INT
USE     szwzcheck             -- 要操作的数据库名
SELECT  @LogicalFileName = 'szwzcheck_Log',  -- 日志文件名
@MaxMinutes = 10,               -- Limit on time allowed to wrap log.
        @NewSize = 20                  -- 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 
      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
 
--把szwzcheck换成你数据库的名字即可，在查询分析器里面运行。

--收缩日志：企业管理器--所有任务--收缩数据库--文件--选日志文件收缩

------解决方案--------------------
这个方法可以在第一步把数据库先分离出来，然后把过大的日志文件删去，
再执行第2步，数据库又可以导回sqlserver中，此时日志文件就是一个全新的小日志文件;

1.  EXEC sp_detach_db @dbname = 'pubs'

2. EXEC sp_attach_single_file_db @dbname = 'pubs',  
   @physname = 'c:\mssql7\data\pubs.mdf'