August 7, 2023

**Summary**: In this tutorial, you will learn how to use the PostgreSQL `ROW_NUMBER()`

function to assign a unique integer value to each row in a result set.

**Table of Contents**

## Introduction to the PostgreSQL `ROW_NUMBER()`

function

The `ROW_NUMBER()`

function is a window function that assigns a sequential integer to each row in a result set. The following illustrates the syntax of the `ROW_NUMBER()`

function:

```
ROW_NUMBER() OVER(
[PARTITION BY column_1, column_2,…]
[ORDER BY column_3,column_4,…]
)
```

The set of rows on which the `ROW_NUMBER()`

function operates is called a window.

The `PARTITION BY`

clause divides the window into smaller sets or partitions. If you specify the `PARTITION BY`

clause, the row number for each partition starts with one and increments by one.

Because the `PARTITION BY`

clause is optional to the `ROW_NUMBER()`

function, therefore you can omit it, and `ROW_NUMBER()`

function will treat the whole window as a partition.

The `ORDER BY`

clause inside the `OVER`

clause determines the order in which the numbers are assigned.

## PostgreSQL `ROW_NUMBER()`

function examples

We will use the `products`

table created in the PostgreSQL window function tutorial to demonstrate the functionality of the `ROW_NUMBER()`

function.

The following is the data in the `products`

table:

See the following query.

```
SELECT
product_id,
product_name,
group_id,
ROW_NUMBER () OVER (ORDER BY product_id)
FROM
products;
```

Because we did not use the `PARTITION BY `

clause, the `ROW_NUMBER()`

function considers the whole result set as a partition.

The `ORDER BY`

clause sorts the result set by `product_id`

, therefore, the `ROW_NUMBER()`

function assigns integer values to the rows based on the `product_id`

order.

In the following query, we change the column in the `ORDER BY`

clause to product_name, the `ROW_NUMBER()`

function assigns the integer values to each row based on the product name order.

```
SELECT
product_id,
product_name,
group_id,
ROW_NUMBER () OVER (
ORDER BY product_name
)
FROM
products;
```

In the following query, we use the `PARTITION BY`

clause to divide the window into subsets based on the values in the `group_id`

column. In this case, the `ROW_NUMBER()`

function assigns one to the starting row of each partition and increases by one for the next row within the same partition.

The `ORDER BY`

clause sorts the rows in each partition by the values in the `product_name`

column.

```
SELECT
product_id,
product_name,
group_id,
ROW_NUMBER () OVER (
PARTITION BY group_id
ORDER BY
product_name
)
FROM
products;
```

## PostgreSQL `ROW_NUMBER()`

function and `DISTINCT`

operator

The following query uses the `ROW_NUMBER()`

function to assign integers to the distinct prices from the `products`

table.

```
SELECT DISTINCT
price,
ROW_NUMBER () OVER (ORDER BY price)
FROM
products
ORDER BY
price;
```

However, the result is not expected because it includes duplicate prices. The reason is that the `ROW_NUMBER()`

operates on the result set before the `DISTINCT`

is applied.

To solve this problem, we can get a list of distinct prices in a CTE, the apply the `ROW_NUMBER()`

function in the outer query as follows:

```
WITH prices AS (
SELECT DISTINCT
price
FROM
products
) SELECT
price,
ROW_NUMBER () OVER (ORDER BY price)
FROM
prices;
```

Or we can use a subquery in the `FROM`

clause to get a list of unique price, and then apply the `ROW_NUMBER()`

function in the outer query.

```
SELECT
price,
ROW_NUMBER () OVER (ORDER BY price)
FROM
(
SELECT DISTINCT
price
FROM
products
) prices;
```

## Using `ROW_NUMBER()`

function for pagination

In application development, you use the pagination technique for displaying a subset of rows instead of all rows in a table.

Besides using the LIMIT clause, you can also use the `ROW_NUMBER()`

function for the pagination.

For example, the following query selects the five rows starting at row number 6:

```
SELECT
*
FROM
(
SELECT
product_id,
product_name,
price,
ROW_NUMBER () OVER (ORDER BY product_name)
FROM
products
) x
WHERE
ROW_NUMBER BETWEEN 6 AND 10;
```

## Using `ROW_NUMBER()`

function for getting the nth highest / lowest row

For example, to get the third most expensive products, first, we get the distinct prices from the products table and select the price whose row number is 3. Then, in the outer query, we get the products with the price that equals the 3rd highest price.

```
SELECT
*
FROM
products
WHERE
price = (
SELECT
price
FROM
(
SELECT
price,
ROW_NUMBER () OVER (
ORDER BY price DESC
) nth
FROM
(
SELECT DISTINCT
(price)
FROM
products
) prices
) sorted_prices
WHERE
nth = 3
);
```

In this tutorial, we have shown you how to use the PostgreSQL `ROW_NUMBER()`

function to assign integer values to rows in a result set.

## See more

PostgreSQL Tutorial: Window Functions

PostgreSQL Documentation: Window Functions