Question

我想在Distance_KM列中找到最大值。这是我的代码...

SELECT Source_Airport, Destination_Airport, Airline, Source_LAT, Source_LONG, Destination_LAT,  Destination_LONG,
(111.045*DEGREES(ACOS(COS(RADIANS(Source_LAT)) * COS(RADIANS(Destination_LAT)) *
             COS(RADIANS(Source_LONG) - RADIANS(Destination_LONG)) +
             SIN(RADIANS(Source_LAT)) * SIN(RADIANS(Destination_LAT))))) as Distance_KM 
FROM  

(SELECT 
    routes.Source_Airport AS Source_Airport,
    routes.Destination_Airport AS Destination_Airport,
    routes.Airline AS Airline,
    S.Latitude AS Source_LAT,
    S.Longitude AS Source_LONG,
    D.Latitude AS Destination_LAT,
    D.Longitude AS Destination_LONG
FROM
    ROUTES
        INNER JOIN
    airports AS S ON S.Airport_ID = routes.Source_Airport_ID
        INNER JOIN
    airports AS D ON D.Airport_ID = routes.Destination_Airport_ID) as Airport_Dist

哪个会生成一个像这样的表...

                                                                  Distance_KM
YYZ YAM AC  43.67720032 -79.63059998    46.48500061 -84.50939941    493.34801024280597
YUL YBC AC  45.47060013 -73.74079895    49.13249969 -68.20439911    582.0897139062885
YYY YBC AC  48.60860062 -68.20809937    49.13249969 -68.20439911    58.1770000072475
YUL YBG AC  45.47060013 -73.74079895    48.33060074 -70.99639893    379.706058161593
YCS YBK 5T  63.34690094 -90.73110199    64.29889679 -96.07779694    282.3404661252172
YRT YBK 5T  62.81140137 -92.11579895    64.29889679 -96.07779694    256.1877034117866
YRT YBK 7F  62.81140137 -92.11579895    64.29889679 -96.07779694    256.1877034117866
YUT YBK 7F  66.52140045 -86.22470093    64.29889679 -96.07779694    517.0880293513636
YQQ YBL 8P  49.71080017 -124.887001 49.95080185 -125.2710037    38.299320607992

要在Distance_KM列中找到最大值，我想我只需要像这样用MAX（）函数包装公式（产生列）...

MAX（ ）（111.045 * DEGREES（ACOS（COS（RADIANS（Source_LAT））* COS（RADIANS（Destination_LAT））* COS（RADIANS（Source_LONG）-RADIANS（Destination_LONG））+ SIN（RADIANS（Source_LAT））* SIN（RADIANS（Destination_LAT））））））作为Distance_KM

我希望脚本返回最远距离的条目，但它会使服务器崩溃。

为什么这不起作用？

Answer 1

很有可能它并没有真正使服务器崩溃-它“只是”让他忙了几个小时，几天或几个月。

这种计算距离的方法不能很好地扩展：它非常耗费计算资源。

您有几种选择：

将CPU与存储进行交易，并创建一个距离表，该距离表通过机场表上的ON AFTER UPDATE，ON AFTER INSERT和ON AFTER DELETE触发器进行维护。这样，您就可以轻松获得距离，几千个机场只会给您几百万个可能的距离。由于机场表不经常更新，因此触发器很可能没有问题。
使用优化的算法：首先根据盒定理计算正交距离（简称差），以创建高度简化的候选表，然后在该表上运行MAX。
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我如何精简代码以防止其使服务器崩溃？

1 个答案: