PostgreSQL – ROW_NUMBER Function

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The ROW_NUMBER() function is used to assign a unique integer to each row within a result set. This function is often used to generate consecutive integers based on the specified ordering criteria. It’s useful for scenarios where you need a sequential identifier for each row, such as ranking, pagination, and generating unique row identifiers.

The syntax of the ROW_NUMBER() function is as follows:

ROW_NUMBER() OVER (PARTITION BY partition_expression ORDER BY sort_expression)
  • PARTITION BY: An optional clause that divides the result set into partitions or groups. The row numbers are generated separately within each partition. If omitted, the row numbers are generated for the entire result set.
  • ORDER BY: Specifies the column(s) by which you want to order the result set for generating row numbers.

Here’s a simple example of how to use the ROW_NUMBER() function in PostgreSQL:

Suppose you have a table named “employees” with columns “employee_id”, “first_name”, and “last_name”, and you want to assign a unique row number to each employee based on their last names:

SELECT employee_id, first_name, last_name, ROW_NUMBER() OVER (ORDER BY last_name) AS row_number FROM employees;

In this example, the ROW_NUMBER() function generates a unique row number for each employee based on the order of their last names. The result might look like this:

employee_id | first_name | last_name | row_number

-------------+------------+-----------+------------

1 | John | Doe | 1

2 | Jane | Smith | 2

3 | David | Johnson | 3

4 | Mary | Williams | 4

5 | Michael | Brown | 5

In this output, the “row_number” column contains the sequential integer assigned to each employee based on the alphabetical order of their last names.

The ROW_NUMBER() function is particularly useful when you need a unique identifier for each row in a result set, especially when you want to maintain a consistent order across different queries or operations.

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