# Covariance

> Supported in: Batch, Streaming

Calculate the population covariance of values in two columns.

**Expression categories:** Aggregate

## Declared arguments

* **Left:** The first column on which covariance is computed.<br>*Expression\<Numeric>*
* **Right:** The second column on which covariance is computed.<br>*Expression\<Numeric>*

**Output type:** *Double*

## Examples

### Example 1: Base case

**Argument values:**

* **Left:** `left`
* **Right:** `right`

**Given input table:**

| left | right |
| ----- | ----- |
| 1 | 5 |
| 2 | 4 |
| 3 | 3 |
| 4 | 2 |
| 5 | 1 |

**Outputs:** -2.0

***

### Example 2: Null case

**Argument values:**

* **Left:** `left`
* **Right:** `right`

**Given input table:**

| left | right |
| ----- | ----- |
| 1.0 | 2.0 |
| *null* | *null* |
| 2.0 | 1.0 |

**Outputs:** -0.25

***