Grouping data into quartiles

The following example demonstrates how to group data into four roughly equal-sized buckets:

/* This finds quartiles in the range
  * of ProductSubCategory, arranged by
  * total sales. Adjust the grouping
  * attribute and metric to your use case.
  */
DEFINE Input AS SELECT
   ProductSubcategoryName AS Key,
   SUM(FactSales_SalesAmount) AS Metric
FROM SaleState
GROUP BY Key
ORDER BY Metric;

DEFINE Quartile1Records AS SELECT
   Key AS Key,
   Metric AS Metric
FROM Input
ORDER BY Metric
PAGE(0, 25) PERCENT;

/* Using MAX(Metric) as the Quartile boundary isn't quite
  * right: if the boundary falls between two records, the
  * quartile is the average of the values on those two records.
  * But this gives the right groupings.
  */
DEFINE Quartile1 AS SELECT
   MAX(Metric) AS Quartile,
   SUM(Metric) AS Metric /* ...or any other aggregate */ 
FROM Quartile1Records 
GROUP;

DEFINE Quartile2Records AS SELECT
   Key AS Key,
   Metric AS Metric
FROM Input
ORDER BY Metric
PAGE(25, 25) PERCENT;

DEFINE Quartile2 AS SELECT
   MAX(Metric) AS Quartile,
   SUM(Metric) AS Metric
FROM Quartile2Records
GROUP;

DEFINE Quartile3Records AS SELECT
   Key AS Key,
   Metric AS Metric
FROM Input
ORDER BY Metric
PAGE(50, 25) PERCENT;

DEFINE Quartile3 AS SELECT
   MAX(Metric) AS Quartile,
   SUM(Metric) AS Metric
FROM Quartile3Records
GROUP;

DEFINE Quartile4Records AS SELECT
   Key AS Key,
   Metric AS Metric
FROM Input
ORDER BY Metric
PAGE(75, 25) PERCENT;

DEFINE Quartile4 AS SELECT
   MAX(Metric) AS Quartile,
   SUM(Metric) AS Metric
FROM Quartile4Records
GROUP;

/**
  * The technical definition of "Quartile" is
  * the values that segment the data into four
  * roughly equal groups. Here, we return not
  * just the Quartiles, but the metric aggregated
  * over the records within the groups defined
  * by the Quartiles.
  */
RETURN Quartiles AS
SELECT
   Quartile AS Quartile1,
   Metric AS Quartile1Metric,
   Quartile2[].Quartile AS Quartile2,
   Quartile2[].Metric AS Quartile2Metric,
   Quartile3[].Quartile AS Quartile3,
   Quartile3[].Metric AS Quartile3Metric,
   Quartile4[].Quartile AS Quartile4,
   Quartile4[].Metric AS Quartile4Metric 
FROM Quartile1;