SQL ROW NUMBER

What is SQL ROW_NUMBER?

SQL ROW_NUMBER is a window function that assigns a unique sequential integer to each row in a result set. This function is useful for ranking or identifying rows within a result set based on a specified order.

When you would use it

You would use the SQL ROW_NUMBER function when you want to:

1. Rank rows: Assign a rank to each row in a result set based on one or more columns' values. For example, ranking products by sales performance.

2. Paginate results: Implement pagination by numbering rows and selecting a specific range of rows from the result set, such as displaying the first 10 rows or the next 20 rows.

3. Remove duplicates: Identify and eliminate duplicate rows by numbering them and selecting only the rows with a row number of 1.

4. Assign unique identifiers: Generate unique identifiers or surrogate keys for rows when creating a new table or merging data from multiple sources.

Syntax

The basic syntax for using the SQL ROW_NUMBER function is as follows:

SELECT
    column1,
    column2,
    ...,
    ROW_NUMBER() OVER (ORDER BY column_to_order) AS row_num
FROM
    your_table;

• column1, column2, ...: The columns you want to retrieve.
• ROW_NUMBER(): The window function that generates the row number.
• ORDER BY column_to_order: The column or columns by which you want to order the rows for numbering.
• row_num: The alias for the row number column.

Parameter values

• column1, column2, ...: The columns you want to include in the result set.
• ORDER BY column_to_order: The column or columns used to determine the order in which rows are numbered.

Example query

Suppose you have a table "products" with columns "product_name" and "sales," and you want to rank products by their sales performance. You can use the ROW_NUMBER function like this:

SELECT
    product_name,
    sales,
    ROW_NUMBER() OVER (ORDER BY sales DESC) AS rank
FROM
    products;

Example table response

Assuming the "products" table contains data like this:

| product_name | sales |
| ------------ | ----- |
| Product A    | 1200  |
| Product B    | 900   |
| Product C    | 1500  |
| Product D    | 800   |

The query mentioned earlier would return the following result:

| product_name | sales | rank |
| ------------ | ----- | ---- |
| Product C    | 1500  | 1    |
| Product A    | 1200  | 2    |
| Product B    | 900   | 3    |
| Product D    | 800   | 4    |

This result ranks products by their sales performance in descending order.

Use cases

• Ranking or ordering rows based on specific criteria.
• Implementing pagination to display a limited number of rows at a time.
• Identifying and removing duplicate rows.
• Generating unique identifiers or surrogate keys for data.

SQL languages this is available for

SQL ROW_NUMBER is a window function available in most modern relational database management systems (RDBMS), including but not limited to:

• SQL Server
• PostgreSQL
• Oracle Database
• MySQL
• SQLite
• IBM Db2
• MariaDB

The syntax and behavior of the ROW_NUMBER function are consistent across these database systems, with minor variations in specific implementations.