# Prometheus Query to Count Unique Label Values

To count unique label values in Prometheus, you can use the `count` function along with the `by` clause to aggregate metrics based on a specific label. This is useful when you want to find out how many unique values a particular label has within a given metric.

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### Example Scenario

Let’s say you have a metric called `http_requests_total` that includes a label named `instance`. You want to count how many unique instances are being tracked.

### PromQL Query

Here’s how you can construct your query:

```
count(http_requests_total) by (instance)
```

### Breakdown of the Query

- **`count(http_requests_total)`**: This part of the query counts the number of occurrences of the `http_requests_total` metric across all instances.
- **`by (instance)`**: This clause specifies that the counting should be grouped by the `instance` label. As a result, you will get a count of `http_requests_total` for each unique `instance`.

### Getting Distinct Unique Values

If you want to get the distinct unique values of a label (rather than just counting how many times each unique value appears), you can use the `count` function on the `label_replace` function. Here’s an example:

```
count(count(http_requests_total) by (instance))
```

### Additional Example: Counting Unique Values of a Different Label

Suppose you want to count unique values of another label, such as `status`, from the same metric:

```
count(http_requests_total) by (status)
```

This will give you the count of requests grouped by the `status` code.

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