AWS SimpleDB - 如何创建偏移量以解决默认结果限制100

Question

AWS SimpleDB的默认结果限制为100，我试图从我的数据库中获取最后20条记录。他们的在线帮助说明：“只要where和order by子句匹配，count（*）和select返回的下一个标记是可以互换的。例如，如果要在第一个10,000之后返回200个项目（类似于偏移量） ），您可以使用限制条款10,000执行计数，并使用下一个标记返回接下来的200项选项。“

所以我正在尝试研究如何执行这两个操作。我首先得到记录数量的计数（在我的例子中约为160），然后我从中减去20以创建偏移量。但AWS仍在返回前100条记录。我假设“// ++”之间的代码在创建偏移时不正确。

            //++ AWS has display limit of 100 so create offset by starting from count - 20 
        NSString *sdbAppOffset = [NSString stringWithFormat:@"select count(*) from %@ limit %i",sdbAppUse,iDbaseRecordCountOffset];

        SimpleDBSelectRequest *selectOffsetRequest = [[SimpleDBSelectRequest alloc] initWithSelectExpression:sdbAppOffset];
        selectOffsetRequest.consistentRead = YES;

        SimpleDBSelectResponse *selectOffSetResponse = [sdbClient select:selectOffsetRequest];
        //NSLog(@"sdbAppUse count %i",[selectOffSetResponse.items count]);

        //++ 

        NSString *sdbAppUseString = [NSString stringWithFormat:@"select * from %@",sdbAppUse];

        SimpleDBSelectRequest *selectRequest = [[SimpleDBSelectRequest alloc] initWithSelectExpression:sdbAppUseString];
        selectRequest.consistentRead = YES;

        SimpleDBSelectResponse *selectResponse = [sdbClient select:selectRequest];
        NSLog(@"sdbAppUse count %i",[selectResponse.items count]);

        for (int x = 0; x < [selectResponse.items count]; x++) { 

            SimpleDBItem *registerUser = [selectResponse.items objectAtIndex:x];

            for (SimpleDBAttribute *attribute in registerUser.attributes) {
                NSLog(@"trackUsage registerUser |%@|, name |%@|, value |%@|",registerUser.name, attribute.name, attribute.value);

            }
        }