Reference

Filling in missing data with sequences of cardinal integers

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When you’re extracting summaries of information from a database, sometimes rows are missing.  For example, if you are keeping track of number of customers by day, you might use a query like this: View the code on Gist. You might get a result set like this: 2014-03-07 122 2014-03-08 355 2014-03-10 234 2014-03-11 119 Notice … Read more

The Vincenty great-circle distance formula

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This Vincenty formula is a more numerically stable version of the spherical cosine law formula (commonly and wrongly known as the Haversine formula) for computing great circle distances. The question of numerical stability comes up specifically when the distances between points are small. In those cases the cosine is very close to 1, so the … Read more

SQL Reporting by time intervals

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A version of this article specific to the Oracle DBMS is here. It’s often helpful to use SQL to group information by periods of time. For example, we might like to examine sales data. For example, we might have a table of individual sales transactions like so. Sales: sales_id int sales_time datetime net decimal(7,2) tax … Read more

Stored function for haversine distance computation

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In another article I described the process of using MySQL to compute great-circle distances between various points on the earth then their latitudes and longitudes are known.  To do this requires the formula commonly called the haversine formula. It’s actually the spherical cosine law formula, and is shown here. There’s a more numerically stable formula — … Read more