SKEW,SKEW_POP,SKEWNESS

skewness,skew,skew_pop

描述

返回表达式的 斜度。 用来计算斜度的公式是 3阶中心矩 / ((方差)^{1.5}), 当方差为零时, skewness 会返回 NULL.

语法

skewness(expr)

参数说明

TinyInt/SmallInt/Integer/BigInt/Float/Double, Decimal 会被 cast 成浮点数参与运算。

返回值说明

Double

举例

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 | 1.1543940205711711 |
+--------------------+--------------------+
1 row in set (0.01 sec)

// 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 |
+------------+------------+
5 rows in set (0.04 sec)

相关命令

kurt