The *PERCENT_RANK()* function is a window function in SQL that calculates the relative rank of each row within a result set as a percentage. It provides a way to understand the distribution of row values in relation to the other rows in the dataset.
The formula for *PERCENT_RANK()* is:
PERCENT_RANK() = (RANK() - 1) / (N - 1)

Where:
- *RANK()* is the rank of the current row.
- *N* is the total number of rows in the result set.
The *PERCENT_RANK()* function returns a value ranging from 0 to 1, inclusive. The lowest rank returns 0, while the highest rank returns just below 1 (which translates to the percentage of rows below that rank).
###### Syntax

The syntax for using *PERCENT_RANK()* is as follows:
PERCENT_RANK() OVER (PARTITION BY partition_expression ORDER BY order_expression)

- *PARTITION BY* (optional): Divides the result set into partitions to which the function is applied. If omitted, the entire result set is treated as a single partition.
- *ORDER BY*: Defines the logical order of the rows in each partition.
###### Example

Suppose you have a table named *Employees* with a column *Salary*. To calculate the percent rank of each employee's salary, you would write a query like this:
SELECT
EmployeeID,
Salary,
PERCENT_RANK() OVER (ORDER BY Salary) AS SalaryPercentRank
FROM
Employees;

###### Explanation of Example

1. **SELECT Statement**: You are selecting the *EmployeeID*, *Salary*, and the calculated *SalaryPercentRank*.
2. **PERCENT_RANK()**: The function calculates the percent rank for each employee based on their salary.
3. **ORDER BY Salary**: The rows are ordered by the *Salary* column to determine the ranking.
###### Result Interpretation

- The output will show each employee's ID, their salary, and their percent rank:
- If an employee ranks lowest in salary, their *SalaryPercentRank* will be *0*.
- If an employee ranks highest, their *SalaryPercentRank* will be close to *1*, indicating their position relative to all other salaries.
###### Notes

- Remember that *PERCENT_RANK()* will return the same value for rows with the same rank.
- If you partition the data (using *PARTITION BY*), the percent rank will be calculated within those partitions.
This powerful function helps in statistical analysis and understanding the distribution of values in your datasets.