KURT,KURT_POP,KURTOSIS
描述
kurtosis 返回 expr 表达式的峰度值。此函数使用的公式为 第四阶中心矩 / (方差的平方) - 3，当方差为零时，kurtosis 将返回 NULL。
语法
kurtosis(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 值会被忽略
select kurt(val1), kurt(val2) from statistic_test;
--------------
+-------------------+--------------------+
| kurt(val1) | kurt(val2) |
+-------------------+--------------------+
| 0.162124583734851 | -1.3330994719286338 |
+-------------------+--------------------+
1 row in set (0.02 sec)
// 每组只有一行数据，结果为 NULL
select kurt(val1), kurt(val2) from statistic_test group by tag;
--------------
+------------+------------+
| kurt(val1) | kurt(val2) |
+------------+------------+
| NULL | NULL |
| NULL | NULL |
| NULL | NULL |
| NULL | NULL |
| NULL | NULL |
+------------+------------+
5 rows in set (0.02 sec)
