PERCENTILE_CONT function [Analytical]

Function

Given a percentile, returns the value that corresponds to that percentile. Assumes a continuous distribution data model.

NoteIf you are simply trying to compute a percentile, use the NTILE function instead, with a value of 100.

Syntax

PERCENTILE_CONT ( expression1 )
WITHIN GROUP ( ORDER BY expression2 [ ASC | DESC ] )

Parameters

expression1 A constant of numeric data type and range from 0 to 1 (inclusive). If the argument is NULL, a “wrong argument for percentile” error is returned. If the argument value is less than 0 or greater than 1, a “data value out of range” error is returned.

expression2 A sort specification that must be a single expression involving a column reference. Multiple expressions are not allowed and no rank analytical functions, set functions, or subqueries are allowed in this sort expression.

Example

The following example uses the PERCENTILE_CONT function to determine the 10th percentile value for car sales in a region.

The following data set is used in the example:

sales       region        dealer_name
900         Northeast     Boston
800         Northeast     Worcester
800         Northeast     Providence
700         Northeast     Lowell
540         Northeast     Natick
500         Northeast     New Haven
450         Northeast     Hartford
800         Northwest     SF
600         Northwest     Seattle
500         Northwest     Portland
400         Northwest     Dublin
500         South         Houston
400         South         Austin
300         South         Dallas
200         South         Dover

The following SELECT statement contains the PERCENTILE_CONT function:


SELECT region, PERCENTILE_CONT(0.1)
WITHIN GROUP ( ORDER BY sales DESC )
FROM carSales GROUP BY region;

The result of the SELECT statement lists the 10th percentile value for car sales in a region:

region           percentile_cont
Northeast        840
Northwest        740
South            470

Usage

The inverse distribution analytical functions return a k-th percentile value, which can be used to help establish a threshold acceptance value for a set of data. The function PERCENTILE_CONT takes a percentile value as the function argument, and operates on a group of data specified in the WITHIN GROUP clause, or operates on the entire data set. The function returns one value per group. If the GROUP BY column from the query is not present, the result is a single row. The data type of the results is the same as the data type of its ORDER BY item specified in the WITHIN GROUP clause. The data type of the ORDER BY expression for PERCENTILE_CONT must be numeric.

PERCENTILE_CONT requires a WITHIN GROUP (ORDER BY) clause.

The ORDER BY clause, which must be present, specifies the expression on which the percentile function is performed and the order in which the rows are sorted in each group. For the PERCENTILE_CONT function, the data type of this expression must be numeric. This ORDER BY clause is used only within the WITHIN GROUP clause and is not an ORDER BY for the SELECT.

The WITHIN GROUP clause distributes the query result into an ordered data set from which the function calculates a result. The WITHIN GROUP clause must contain a single sort item. If the WITHIN GROUP clause contains more or less than one sort item, an error is reported.

The ASC or DESC parameter specifies the ordering sequence ascending or descending. Ascending order is the default.

The PERCENTILE_CONT function is allowed in a subquery, a HAVING clause, a view, or a union. PERCENTILE_CONT can be used anywhere the simple nonanalytical aggregate functions are used. The PERCENTILE_CONT function ignores the NULL value in the data set.

Standards and compatibility

See also

“Analytical functions”

“NTILE function [Analytical]”

“PERCENTILE_DISC function [Analytical]”

Chapter 4, “Using OLAP” in the Sybase IQ Performance and Tuning Guide