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# PostgreSQL NTILE Function

**Summary**: in this tutorial, you will learn how to use the PostgreSQL `NTILE()` function to divide ordered rows in the partition into a specified number of ranked buckets.

## Introduction to PostgreSQL NTILE() function

The PostgreSQL `NTILE()` function allows you to divide ordered rows in the partition into a specified number of ranked groups as equal size as possible. These ranked groups are called buckets.

The `NTILE()` function assigns each group a bucket number starting from 1. For each row in a group, the `NTILE()` function assigns a bucket number representing the group to which the row belongs.

The syntax of the `NTILE()` function is as follows:

```sql
NTILE(buckets) OVER (
    [PARTITION BY partition_expression, ... ]
    [ORDER BY sort_expression [ASC | DESC], ...]
)

```

Let's examine the syntax in detail:

### buckets

The `buckets` represents the number of ranked groups. It can be a number or an expression that evaluates to a positive integer value (greater than 0) for each partition. The `buckets` must not be nullable.

### PARTITION BY

The `PARTITION BY` clause distributes rows into partitions to which the function is applied.

The `PARTITION BY` clause is optional. If you skip it, the function treats the whole result set as a single partition.

### ORDER BY

The `ORDER BY` clause sorts rows in each partition to which the function is applied.

The `ORDER BY` clause is optional. However, you should always use the `ORDER BY` clause to get an expected result.

Note that if the number of rows is not divisible by the `buckets`, the `NTILE()` function returns groups of two sizes with the difference by one. The bigger groups always come before the smaller groups in the order specified by the `ORDER BY` clause.

## PostgreSQL NTILE() function examples

Let's take some examples of using the `NTILE()` function.

We'll use the `sales_stats` table created in the [`CUME_DIST()`](https://neon.com/postgresql/postgresql-window-function/postgresql-cume_dist-function) function tutorial to demonstrate the `NTILE()` function.

```sql
SELECT
	year,
	name,
	amount
FROM
	actual_sales
ORDER BY
	year, name;
```

![sales\_stats table](https://neon.com/postgresqltutorial/sales_stats-table.png)

### 1) Using PostgreSQL NTILE() function over a result set example

This example uses the `NTILE()` function to distribute rows into 3 buckets:

```sql
SELECT
	name,
	amount,
	NTILE(3) OVER(
		ORDER BY amount
	)
FROM
	sales_stats
WHERE
	year = 2019;

```

Here is the output:

![PostgreSQL NTILE Function Over a Result Set Example](https://neon.com/postgresqltutorial/PostgreSQL-NTILE-Function-Over-a-Result-Set-Example.png)

### 2) Using PostgreSQL NTILE() function over a partition example

This example uses the `NTILE()` function to divide rows in the `sales_stats` table into two partitions and 3 buckets for each:

```sql
SELECT
	name,
	amount,
	NTILE(3) OVER(
		PARTITION BY year
		ORDER BY amount
	)
FROM
	sales_stats;

```

Here is the result set:

![PostgreSQL NTILE Function Over a Partition Example](https://neon.com/postgresqltutorial/PostgreSQL-NTILE-Function-Over-a-Partition-Example.png)
In this tutorial, you have learned how to use the PostgreSQL `NTILE()` function to distribute ordered rows within a partition into a specified number of ranked groups.

---

## Related docs (Window Functions)

- [CUME_DIST](https://neon.com/postgresql/postgresql-window-function/postgresql-cume_dist-function)
- [DENSE_RANK](https://neon.com/postgresql/postgresql-window-function/postgresql-dense_rank-function)
- [FIRST_VALUE](https://neon.com/postgresql/postgresql-window-function/postgresql-first_value-function)
- [LAG](https://neon.com/postgresql/postgresql-window-function/postgresql-lag-function)
- [LAST_VALUE](https://neon.com/postgresql/postgresql-window-function/postgresql-last_value-function)
- [LEAD](https://neon.com/postgresql/postgresql-window-function/postgresql-lead-function)
- [NTH_VALUE](https://neon.com/postgresql/postgresql-window-function/postgresql-nth_value-function)
- [PERCENT_RANK](https://neon.com/postgresql/postgresql-window-function/postgresql-percent_rank-function)
- [RANK](https://neon.com/postgresql/postgresql-window-function/postgresql-rank-function)
- [ROW_NUMBER](https://neon.com/postgresql/postgresql-window-function/postgresql-row_number)