SQL Row_number

Galaxy Glossary

How can I assign a unique sequential number to each row in a result set?

The ROW_NUMBER() window function assigns a unique sequential integer to each row within a partition of a result set, ordered by specified columns. It's crucial for tasks like pagination, ranking, and identifying specific rows.

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Description

Table of Contents

The ROW_NUMBER() window function is a powerful tool in SQL for generating sequential numbers for rows within a result set. Unlike aggregate functions that operate on groups of rows, ROW_NUMBER() assigns a unique number to each individual row. This is particularly useful for tasks like creating a unique identifier for each row, ordering rows within a partition, or selecting specific rows based on their position. For instance, imagine you need to paginate results from a large table. ROW_NUMBER() can help you select a specific range of rows. Another use case is assigning unique IDs to rows in a table, which can be helpful for tracking changes or for joining with other tables. The function operates within a window, meaning it considers only the rows that meet the specified criteria within a partition. This allows for independent numbering within different groups of data.

Why SQL Row_number is important

ROW_NUMBER() is essential for tasks requiring ordered results within a partition. It's a fundamental tool for data analysis, reporting, and data manipulation, enabling developers to extract specific rows based on their position within a set.

SQL Row_number Example Usage


CREATE TABLE Employees (
    EmployeeID INT PRIMARY KEY,
    EmployeeName VARCHAR(255),
    ManagerID INT,
    Salary DECIMAL(10, 2)
);

INSERT INTO Employees (EmployeeID, EmployeeName, ManagerID, Salary)
VALUES
    (1, 'John Doe', NULL, 60000),
    (2, 'Jane Smith', 1, 55000),
    (3, 'Peter Jones', 1, 65000),
    (4, 'David Lee', 2, 45000),
    (5, 'Emily Brown', 3, 50000);

WITH RECURSIVE EmployeeHierarchy AS (
    SELECT EmployeeID, EmployeeName, ManagerID, Salary
    FROM Employees
    WHERE ManagerID IS NULL
    UNION ALL
    SELECT e.EmployeeID, e.EmployeeName, e.ManagerID, e.Salary
    FROM Employees e
    JOIN EmployeeHierarchy eh ON e.ManagerID = eh.EmployeeID
)
SELECT EmployeeID, EmployeeName, ManagerID, Salary
FROM EmployeeHierarchy;

SQL Row_number Syntax



Common Mistakes

Frequently Asked Questions (FAQs)

How does ROW_NUMBER() differ from traditional aggregate functions like COUNT() or SUM()?

Aggregate functions merge multiple rows into a single result (e.g., COUNT(*) returns one number for an entire group). ROW_NUMBER(), on the other hand, keeps every row intact and simply tags each one with a consecutive integer based on the ORDER BY clause in its window. This makes it ideal when you need to preserve individual rows but still determine their relative position in a set.

What is a practical way to use ROW_NUMBER() for paginating large result sets?

A common pattern is to wrap your query in a CTE that calculates ROW_NUMBER() OVER (ORDER BY some_column), then return only rows where the generated row number falls between two bounds (e.g., 219 for page 3 with a page size of 20). This approach avoids the performance issues of large OFFSET values. In Galaxys SQL editor, the AI copilot can even scaffold this pagination query for you, letting you adjust the page size or sorting column with a few keystrokes.

Why assign unique IDs with ROW_NUMBER() instead of adding an auto-increment column, and what role does PARTITION BY play?

ROW_NUMBER() shines when you need temporary or context-specific identifiers2for example, numbering sales transactions only within each customer or ranking daily events without altering the underlying table schema. Using PARTITION BY customer_id (or any logical group) resets the count for every partition, giving you independent sequences. This flexibility lets you track changes, perform deduplication, or create merge keys on the flyand Galaxys modern IDE helps you experiment quickly without touching production schemas.

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