PERCENTILE_CONT [Analytic]

An inverse distribution function where, for each row, PERCENTILE_CONT returns the value that would fall into the specified percentile among a set of values in each partition within a window. For example, if the argument to the function is 0.5, the result of the function is the median of the data set (50th percentile). PERCENTILE_CONT assumes a continuous distribution data model. NULL values are ignored.

PERCENTILE_CONT computes the percentile by first computing the row number where the percentile row would exist. For example:

row‑number = 1 + percentile‑value * (num‑partition‑rows -1)

If row‑number is a whole number (within an error of 0.00001), the percentile is the value of row row‑number.

Otherwise, Vertica interpolates the percentile value between the value of the CEILING(row‑number) row and the value of the FLOOR(row‑number) row. In other words, the percentile is calculated as follows:

( CEILING( row‑number) - row‑number ) * ( Value of FLOOR(row‑number) row ) 
 + ( row‑number - FLOOR(row‑number) ) * ( Value of CEILING(row‑number) row)

If the percentile value is 0.5, PERCENTILE_CONT returns the same result set as the function MEDIAN.

Behavior Type

Immutable

Syntax

PERCENTILE_CONT ( percentile ) WITHIN GROUP ( ORDER BY expression [ ASC | DESC ] ) OVER ( 
... [ window-partition-clause ] )

Parameters

percentile

Percentile value, a FLOAT constant that ranges from 0 to 1 (inclusive).
WITHIN GROUP(ORDER BY expression)

Specifies how to sort data within each group. ORDER BY takes only one column/expression that must be INTEGER, FLOAT, INTERVAL, or NUMERIC data type. NULL values are discarded.

The WITHIN GROUP(ORDER BY) clause does not guarantee the order of the SQL result. To order the final result , use the SQL ORDER BY clause set.
ASC | DESC

Specifies the ordering sequence as ascending (default) or descending.

Specifying ASC or DESC in the WITHIN GROUP clause affects results as long as the percentile is not 0.5.
OVER()

See Analytic Functions

Examples

This query computes the median annual income per group for the first 300 customers in Wisconsin and the District of Columbia. 

=> SELECT customer_state, customer_key, annual_income,
      PERCENTILE_CONT(0.5) WITHIN GROUP(ORDER BY annual_income) 
      OVER (PARTITION BY customer_state) AS PERCENTILE_CONT
   FROM customer_dimension
   WHERE customer_state IN ('DC','WI')
   AND customer_key < 300
   ORDER BY customer_state, customer_key;
 customer_state | customer_key | annual_income | PERCENTILE_CONT
----------------+--------------+---------------+-----------------
 DC             |           52 |        168312 |        483266.5
 DC             |          118 |        798221 |        483266.5
 WI             |           62 |        283043 |          377691
 WI             |          139 |        472339 |          377691
(4 rows)

This query computes the median annual income per group for all customers in Wisconsin and the District of Columbia. 

=> SELECT customer_state, customer_key, annual_income,
      PERCENTILE_CONT(0.5) WITHIN GROUP(ORDER BY annual_income) 
      OVER (PARTITION BY customer_state) AS PERCENTILE_CONT
   FROM customer_dimension
   WHERE customer_state IN ('DC','WI')
   ORDER BY customer_state, customer_key;
 customer_state | customer_key | annual_income | PERCENTILE_CONT
----------------+--------------+---------------+-----------------
 DC             |           52 |        168312 |        483266.5
 DC             |          118 |        798221 |        483266.5
 DC             |          622 |        220782 |          555088
 DC             |          951 |        178453 |          555088
 DC             |          972 |        961582 |          555088
 DC             |         1286 |        760445 |          555088
 DC             |         1434 |         44836 |          555088
.
.
.
 WI             |           62 |        283043 |          377691
 WI             |          139 |        472339 |          377691
 WI             |          359 |         42242 |          517717
 WI             |          364 |        867543 |          517717
 WI             |          403 |        509031 |          517717
 WI             |          455 |         32000 |          517717
 WI             |          485 |        373129 |          517717
.
.
.
(1353 rows)

See Also