# quantile

[Read this page in HTML](https://www.scopedb.io/docs/reference/functions/aggregate/quantile)

Returns an exact quantile of finite floating-point values.

## Syntax

```scopeql
quantile(<expr>, quantile => <quantile>)
```

## Arguments

| Argument   | Type    | Description                                                  |
| ---------- | ------- | ------------------------------------------------------------ |
| `<expr>`   | `float` | Values to summarize. Cast integer columns to `float` first.  |
| `quantile` | `float` | Constant. Quantile from 0 to 1, inclusive. Must not be NULL. |

## Returns

Returns `float`.

* Ignores NULL values, `NaN`, and infinities. Returns NULL if no finite values remain.
* Selects a value from the input ordered from least to greatest, without interpolation. For `N` values, the position is `max(1, ceil(N * quantile))`, counting from 1.

## Examples

### Compare typical and tail latency

Calculate the p50, p90, and p99 latency of 20 checkout requests in one result. The input values are milliseconds.

```scopeql
VALUES
    (82.0), (88.0), (91.0), (95.0), (98.0),
    (102.0), (108.0), (112.0), (118.0), (125.0),
    (132.0), (140.0), (155.0), (180.0), (210.0),
    (260.0), (340.0), (480.0), (850.0), (1600.0)
SELECT $0 AS latency_ms
AGGREGATE
    quantile(latency_ms, quantile => 0.50) AS p50_ms,
    quantile(latency_ms, quantile => 0.90) AS p90_ms,
    quantile(latency_ms, quantile => 0.99) AS p99_ms
```

```text
+--------+--------+--------+
| p50_ms | p90_ms | p99_ms |
+--------+--------+--------+
| 125.0  | 480.0  | 1600.0 |
+--------+--------+--------+
```

Half the requests took at most 125 ms, while the slowest took 1600 ms. Each percentile selects an observed latency.

### Compare checkout channels

Compare p50 and p95 request latency for web and mobile checkout:

```scopeql
VALUES
    ('web', 90.0), ('web', 110.0), ('web', 150.0), ('web', 320.0),
    ('mobile', 130.0), ('mobile', 190.0), ('mobile', 420.0), ('mobile', 1200.0)
SELECT $0 AS channel, $1 AS latency_ms
GROUP BY channel
AGGREGATE
    quantile(latency_ms, quantile => 0.50) AS p50_ms,
    quantile(latency_ms, quantile => 0.95) AS p95_ms
ORDER BY channel
```

```text
+---------+--------+--------+
| channel | p50_ms | p95_ms |
+---------+--------+--------+
| mobile  | 190.0  | 1200.0 |
| web     | 110.0  | 320.0  |
+---------+--------+--------+
```