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> Reference material for PERCENT_RANK window function

# PERCENT_RANK OVER

Calculates the relative rank of the current row within an ordered data set, as
`( rank - 1 ) / ( rows - 1 )`
where rank is the current row's rank within the partition, and rows is the number of rows in the partition. PERCENT\_RANK always returns values from 0 to 1 inclusive. The first row in any set has a `PERCENT_RANK` of 0.

## Syntax

```sql theme={"theme":{"light":"github-light","dark":"github-dark"}}
PERCENT_RANK() OVER ( [ PARTITION BY <partition_by> ] ORDER BY <order_by> [ASC|DESC] )
```

## Parameters

| Parameter        | Description                                     | Supported input types |
| :--------------- | :---------------------------------------------- | :-------------------- |
| Parameter        | Description                                     |                       |
| `<partition_by>` | An expression used for the partition by clause. | Any                   |
| `<order_by>`     | An expression used for the order by clause.     | Any                   |

## Return Type

`DOUBLE PRECISION`

This function respects `NULL` values, and results will be ordered with default null ordering `NULLS LAST` unless otherwise specified in the `ORDER BY` clause.

## Example

The example below calculates, for each student in grade nine, the percent rank of the student's test score by their grade level.

```sql theme={"theme":{"light":"github-light","dark":"github-dark"}}
SELECT
	nickname, current_score,
	PERCENT_RANK() OVER (PARTITION BY level ORDER BY current_score DESC) as percent_rank
FROM
	class_test
WHERE grade_level=9;
```

**Returns**:

| nickname    | current\_score | percent\_rank |
| :---------- | :------------- | :------------ |
| kennethpark | 90             | 0             |
| sabrina21   | 85             | 0.2           |
| rileyjon    | 80             | 0.4           |
| ymatthews   | 79             | 0.6           |