Question

我有一些查询可以返回较大的结果集（> 10万行）。我需要向用户显示结果数，并且用户能够在我们的应用程序中浏览结果。但是，当页面上显示25时，没有人会翻阅100K项。因此，我希望将可分页结果的数量限制为5K，同时仍向用户显示结果的总数。

当然，我可以向数据库触发两个单独的查询：一个对所有结果进行计数，一个返回TOP（5000）。但是查询可能很昂贵。

是否存在将这两个查询合并为一个聪明的方法？下面的查询过于简化：

close all;
clc;

% read image 
[embededimage_fname, image_pthname] = ...
    uigetfile('*.jpg; *.png; *.tif; *.bmp', 'Select the Cover Image');
if (embededimage_fname ~= 0)
    embedded_image = strcat(image_pthname, embededimage_fname);
    embedded_image = double( rgb2gray( imread( embedded_image ) ) );
    embedded_image = imresize(embedded_image, [512 512], 'bilinear');
else
    return;
end
% read audio
[watermarkAudio_fname, watermark_pthname] = ...
    uigetfile('*.wav', 'Select the Watermark audio');
if (watermarkAudio_fname ~= 0)
    watermark_audio = strcat(watermark_pthname, watermarkAudio_fname);
    [n, fs] = audioread(watermark_audio);            % "n" is number of  samples and fs is the sample rate 
    %watermark_audio = imresize(watermark_audio, [512 512], 'bilinear');
else
    return;
end
imbin_seq = reshape(dec2bin(embedded_image, 8) - '0', 1, []);

% To calculate modified mean
na = 2^15;
n = n*na;
nLength = length(n);
modified_mean = mean(abs(n));

% Embedding Range
lmda = 2.4;    %pick any value of lmda from the range (2.0, 2.5);
e_range = ceil(lmda * modified_mean);

%number of bins and Bin Width
h = histogram(n);
Bin_Num = h.NumBins();
Bin_Width = h.BinWidth();

有人可以帮忙吗？

Answer 1

交叉加入

1602.720000

Answer 2

您可以在下面尝试

func assetDownload(for item: DownloadItem) {

    let asset = AVURLAsset(url: item.url)

    asset.resourceLoader.preloadsEligibleContentKeys = true
    asset.resourceLoader.setDelegate(self, queue: DispatchQueue.global(qos: .default))


    // Create new AVAssetDownloadTask for the desired asset
    guard let task = downloadSession.makeAssetDownloadTask(asset: asset,
                                                           assetTitle: item.title!,
                                                           assetArtworkData: data,
                                                           options: [AVAssetDownloadTaskMinimumRequiredMediaBitrateKey: 2_787_000])
        else {
            status[item.url!] = .error
            return
    }

    task.taskDescription = item.title!

    // Start task and begin download
    task.resume()
}

Answer 3

您可以尝试以下查询：

SELECT TOP 5000 *, 
          COUNT(*) 
               OVER(ORDER BY (SELECT NULL)) 
FROM   table 
WHERE  field = 1;

获取结果数但结果集的一部分

3 个答案: