August 7, 2023

**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:

```
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()`

function tutorial to demonstrate the `NTILE()`

function.

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

### 1) Using PostgreSQL `NTILE()`

function over a result set example

This example uses the `NTILE()`

function to distribute rows into 3 buckets:

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

Here is the output:

### 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:

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

Here is the result set:

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.