docs/sql-manual/sql-functions/aggregate-functions/skew.md

---
{
    "title": "SKEW,SKEW_POP,SKEWNESS",
    "language": "en"
}
---

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## skewness,skew,skew_pop
### Description

Returns the [skewness](https://en.wikipedia.org/wiki/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`.

### Syntax

`skewness(expr)`

### Arguments

TinyInt/SmallInt/Integer/BigInt/Float/Double, Decimal will be casted to a float number.

### Return value

`Double`

### Example
```sql
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)
```
### Related Commands

[kurt](./kurt.md)