# percentile_cont

Calculates a continuous numeric percentile. When the requested position falls
between two values, the result is interpolated between them. `NULL` values are
skipped.

**Syntax**

```text
percentile_cont(fraction) WITHIN GROUP (ORDER BY value [ASC|DESC])
percentile_cont(fraction, value[, descending])
```

**Arguments**

* `fraction` — A number from zero through one, independent of the group's input
  rows. It is validated even when the input is empty.
* `value` — A numeric expression. `NULL` values are skipped.
* `descending` — An optional constant boolean selecting descending order in
  the direct form. The default order is ascending.

Use `FILTER` to select input rows. Array fractions, interval values, and window
calls with `OVER` are not supported.

**Returned value**

A `REAL` percentile, or `NULL` for a `NULL` fraction or no non-`NULL` inputs.

**Examples**

```sql
CREATE TABLE readings (value Int32);
INSERT INTO readings VALUES (10), (20), (30), (40), (NULL);
```

```sql
SELECT percentile_cont(0.5) WITHIN GROUP (ORDER BY value)
FROM readings
FORMAT csv;
```

```text
25.0
```