Raymond Raymond

Spark SQL - PERCENT_RANK Window Function

event 2021-10-18 visibility 1,984 comment 0 insights toc
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About PERCENT_RANK function

PERCENT_RANK in Spark returns the percentile of rows within a window partition.  

PERCENT_RANK without partition

The following sample SQL uses PERCENT_RANK function without PARTITION BY clause:

SELECT StudentScore.*, PERCENT_RANK() OVER (ORDER BY Score) AS Percentile FROM VALUES 
(101,56),
(102,78),
(103,70),
(104,93),
(105,95),
(106,95),
(107,75),
(108,81),
(109,66),
(110,73)
AS StudentScore(Student,Score)

Result:

+-------+-----+------------------+
|Student|Score| Percentile|
+-------+-----+------------------+
| 101| 56| 0.0|
| 109| 66|0.1111111111111111|
| 103| 70|0.2222222222222222|
| 110| 73|0.3333333333333333|
| 107| 75|0.4444444444444444|
| 102| 78|0.5555555555555556|
| 108| 81|0.6666666666666666|
| 104| 93|0.7777777777777778|
| 105| 95|0.8888888888888888|
| 106| 95|0.8888888888888888|
+-------+-----+------------------+
warning The following warning message will show: WARN window.WindowExec: No Partition Defined for Window operation! Moving all data to a single partition, this can cause serious performance degradation. 

PERCENT_RANK with partition

The following sample SQL returns a rank number for each records in each window (defined by PARTITION BY):

SELECT StudentScore.*, PERCENT_RANK() OVER (PARTITION BY Class ORDER BY Score) AS Percentile FROM VALUES 
(1,101,56),
(1,102,78),
(1,103,70),
(1,104,93),
(1,105,95),
(2,106,95),
(2,107,75),
(2,108,81),
(2,109,66),
(2,110,73)
AS StudentScore(Class,Student,Score)

Result:

+-----+-------+-----+----------+
|Class|Student|Score|Percentile|
+-----+-------+-----+----------+
| 1| 101| 56| 0.0|
| 1| 103| 70| 0.25|
| 1| 102| 78| 0.5|
| 1| 104| 93| 0.75|
| 1| 105| 95| 1.0|
| 2| 109| 66| 0.0|
| 2| 110| 73| 0.25|
| 2| 107| 75| 0.5|
| 2| 108| 81| 0.75|
| 2| 106| 95| 1.0|
+-----+-------+-----+----------+

Records are allocated to windows based on Class column and the rank is computed based on column Score.  

infoBy default, records will be sorted in ascending order. Use ORDER BY .. DESC to sort records in descending order.

Example table

The virtual table/data frame is cited from SQL - Construct Table using Literals.

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