所以，一个connect执行完之后要么close，要么自己处理临时文件。

处理方法：在每次执行完数据库操作后close连接，在新执行数据库操作前再open.

		[db open];
		
        [db beginTransaction];
        NSString * insertsql = [self sql:@"INSERT OR IGNORE INTO %@ (`userid`,`friendid`,`isrecommend`,`isfavorite`,`isonline`,`isblock`,`isfriend`,`lastlogintime`,`lastintouchtime`,`distance`) VALUES (?,?,?)" inTable:TABLE_NAME];
        [db executeUpdate:insertsql,userid,friendid,isrecommend,isfavorite,isonline,isblock,isfriend,lastlogintime,lastintouchtime,distance];
        NSInteger lastInsertId = [db lastInsertRowId];
        NSString * updatesql = [self sql:@"UPDATE %@ SET userid=?,friendid=?,isrecommend=?,isfavorite=?,isonline=?,isblock=?,isfriend=?,lastlogintime=?,lastintouchtime=?,distance=? WHERE `index`=?" inTable:TABLE_NAME];
        [db executeUpdate:updatesql,distance,[NSNumber numberWithInt:lastInsertId]];
        [db commit];
		
		[db close];