set_expression is an expression that evaluates to a set, typically a set of members or tuples.
optional_numeric_expression is a numeric-valued expression that the function evaluates for each set element.
Typically, this expression has the form [MEASURES].[measure_name]
If you do not specify a numeric expression, the system uses the measure used by the current result cell. For example, this might be the measure used on the 0 axis or the measure specified in the WHERE clause, if any. If the query itself does not specify a measure, the system instead uses %COUNT, which counts records in the fact table.
optional_percentile_value is a numeric literal that represents the percentile to find. For example, use 30 to find the 30th percentile, which is the value that is greater than 30 percent of the other values.
If you omit this argument, the system computes the 50th percentile.
The function evaluates the numeric value for each element of the set and returns the value that is at the given percentile.
For reference, the following query shows the Patient Count measure for the members of the aged.year level. The ORDER function sorts these members into order by their value of Patient Count so that we can easily compare the later results to this query:
SELECT MEASURES.[%COUNT] ON 0, ORDER(birthd.year.MEMBERS,MEASURES.[%COUNT],BASC) ON 1 FROM patients
1 1916 1
2 1921 1
3 1922 1
4 1925 1
5 1941 1
6 1914 2
82 1967 18
83 1969 18
84 1973 18
85 1978 18
86 1979 18
87 1981 18
88 2002 18
89 2009 18
90 1968 19
91 1998 21
92 1991 23
93 2003 23
94 1977 25
Next, the following query shows the 5th percentile value for these members:
SELECT MEASURES.[%COUNT] ON 0, PERCENTILE(birthd.year.MEMBERS,,5) ON 1 FROM patients
5 Percentile 1
That is, the 5th percentile consists of birth years that have at most 1 patient.
The following query shows the 95th percentile instead:
SELECT MEASURES.[%COUNT] ON 0, PERCENTILE(birthd.year.MEMBERS,,95) ON 1 FROM patients
95 Percentile 18
That is, the 95th percentile consists of birth years that have 18 or fewer patients.
For another example, we use the second argument for PERCENTILE:
SELECT PERCENTILE(birthd.year.MEMBERS,MEASURES.[%COUNT],50) ON 1 FROM patients
50 Percentile 10
For additional, similar examples, see AVG.