我有一栏:城市、x、 y
I need to select the distance between all the cities without duplications the results should look like this city1,city2,distance
but I shouldn t get city2,city1,distance ( since I already got the distance between those cities...
what is the correct SQL query for that... thanks!
SELECT c1.City, c2.City, dbo.CalcDistance(c1.x, c1.y, c2.x, c2.y)
FROM Cities c1, Cities c2
WHERE c1.CityID > c2.CityID
SELECT
C1.city,
C2.city,
<distance calculation>
FROM
Cities C1
INNER JOIN Cities C2 ON
C2.city_id > C1.city_id
我留下了距离计算空白之处,因为它取决于你是否重新“作为代管地”,使用街道路线,核算地球的 cur。
你试图做的是所谓的“总开支”。
与三角合作谨慎,如<代码>ON c1.CityID > c2.CityID,它们制造了一个 car产品! (我不想与任何其他人争辩。)
Have a look at Jeff Moden s world best article about running totals: Solving the "Running Total" & "Ordinal Rank" Problems (Rewritten).
如果你没有的话,你就不得不做一个说明(只需要一个电子邮件地址)。 然而,我承诺这样做是值得的。
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