Categories:: Aggregate functions (General)

SKEW¶

Returns the sample skewness of non-NULL records. If all records inside a group are NULL, the function returns NULL.

The following formula is used to compute the sample skewness:

\[(n^2)/((n-1) * (n-2)) * (m_3/(k_2)^(1.5))\]

where:

\(n\) denotes the number of non-null records.
\(m_3\) denotes the sample third central moment.
\(k_2\) denotes the symmetric unbiased estimator of the variance.

Intuitively, skew describes how asymmetric the underlying distribution is.

Syntax¶

SKEW( <expr> ) 

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Arguments¶

expr: This is an expression that evaluates to a numeric data type (INTEGER, FLOAT, DECIMAL, etc.).

Returns¶

This function returns a value of type DOUBLE.

Usage notes¶

For inputs with fewer than three records, SKEW returns NULL.

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, null),     (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 |  NULL | | 2 | 20.00 | 22.00 | | 2 | 25.00 |  NULL | | 2 | 30.00 | 35.00 | +---+-------+-------+ 

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Query the data:

select SKEW(K), SKEW(V), SKEW(V2)      from aggr; +--------------+---------------+----------+ |      SKEW(K) |       SKEW(V) | SKEW(V2) | |--------------+---------------+----------| | -2.236069766 | 0.05240788515 |     NULL | +--------------+---------------+----------+ 

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