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Given a percentile, returns the value that corresponds to that percentile. Assumes a continuous distribution data model.
If you are simply trying to compute a percentile, use
the NTILE function instead, with a value of 100.
PERCENTILE_CONT ( expression1 ) WITHIN GROUP ( ORDER BY expression2 [ ASC | DESC ] )
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.
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
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.
“PERCENTILE_DISC function [Analytical]”
Chapter 4, “Using OLAP” in the Sybase IQ Performance and Tuning Guide
