SKEW,SKEW_POP,SKEWNESS

Description

Returns the skewness of the expr expression. The forumula used for this function is 3-th centrol moment / ((variance)^{1.5}), when variance is zero, SKEWNESS will return NULL.

Related Commands

kurt

Alias

• SKEW
• SKEW_POP

Syntax

SKEWNESS(<col>)

Parameters

Parameter	Description
<col>	The column to be calculated skewness

Return Value

Returns the skewness of the expr expression, which is a Double type.

Examples

CREATE TABLE statistic_test(
    tag int, 
    val1 double not null, 
    val2 double null
) DISTRIBUTED BY HASH(tag)
PROPERTIES (
    "replication_num"="1"
);

INSERT INTO statistic_test VALUES
(1, -10, -10),
(2, -20, NULL),
(3, 100, NULL),
(4, 100, NULL),
(5, 1000,1000);

-- NULL is ignored
SELECT 
  skew(val1), 
  skew(val2)
FROM statistic_test;

+--------------------+------------+
| skew(val1)         | skew(val2) |
+--------------------+------------+
| 1.4337199628825619 |          0 |
+--------------------+------------+

-- Each group just has one row, result is NULL
SELECT 
  skew(val1), 
  skew(val2) 
FROM statistic_test
GROUP BY tag;

+------------+------------+
| skew(val1) | skew(val2) |
+------------+------------+
|       NULL |       NULL |
|       NULL |       NULL |
|       NULL |       NULL |
|       NULL |       NULL |
|       NULL |       NULL |
+------------+------------+