skewness,skew,skew_pop
描述
返回表达式的 斜度 (opens in a new tab)。
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)