Categories:: Aggregate functions (General) , Window function syntax and usage

KURTOSIS¶

Returns the population excess kurtosis of non-NULL records. If all records inside a group are NULL, the function returns NULL.

The following formula is used to compute the population excess kurtosis:

\[(n * (n+1))/((n-1) * (n-2) * (n-3)) * (n * m_4/(k_2)^2) - 3 * (n-1)^2 / ((n-2) * (n-3))\]

where:

\(n\) denotes the number of non null records.
\(m_4\) denotes the sample fourth central moment.
\(k_2\) denotes the symmetric unbiased estimator of the variance.

Syntax¶

Aggregate function

KURTOSIS( <expr> )

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Window function

KURTOSIS( <expr> ) OVER ( [ PARTITION BY <expr2> ] )

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Arguments¶

expr: This is an expression that evaluates to a numeric data type (INTEGER, FLOAT, DECIMAL, etc.).
expr2: The expression that defines the individual groups or windows.

Returns¶

Returns DOUBLE if the input data type is DOUBLE/FLOAT.

Returns DECIMAL if the input data type is another numeric data type.

Usage notes¶

For inputs with fewer than four records, KURTOSIS returns NULL.

When this function is called as a window function, it does not support:
- An ORDER BY clause within the OVER clause.
- Explicit window frames.

Examples¶

Create a table and load the data:

create or replace table aggr(k int, v decimal(10,2), v2 decimal(10, 2));

insert into aggr values
    (1, 10, null),
    (2, 10, 12),
    (2, 20, 22),
    (2, 25, null),
    (2, 30, 35);

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Display the data:

select *
    from aggr
    order by k, v;
+---+-------+-------+
| K |     V |    V2 |
|---+-------+-------|
| 1 | 10.00 |  NULL |
| 2 | 10.00 | 12.00 |
| 2 | 20.00 | 22.00 |
| 2 | 25.00 |  NULL |
| 2 | 30.00 | 35.00 |
+---+-------+-------+

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Query the data:

select KURTOSIS(K), KURTOSIS(V), KURTOSIS(V2) 
    from aggr;
+----------------+-----------------+--------------+
|    KURTOSIS(K) |     KURTOSIS(V) | KURTOSIS(V2) |
|----------------+-----------------+--------------|
| 5.000000000000 | -2.324218750000 |         NULL |
+----------------+-----------------+--------------+

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