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ROW_NUMBER

Returns a unique row number for each row within a window partition.

The row number starts at 1 and continues up sequentially.

Syntax

ROW_NUMBER() OVER (
[ PARTITION BY <expr1> [, <expr2> ... ] ]
ORDER BY <expr3> [ , <expr4> ... ] [ { ASC | DESC } ]
)

Examples

Suppose we have a table called employees with columns employee_id, first_name, last_name, department, and salary.

We want to number employees within each department based on their salaries in descending order.

Create the table

CREATE TABLE employees (
employee_id INT,
first_name VARCHAR,
last_name VARCHAR,
department VARCHAR,
salary INT
);

Insert data

INSERT INTO employees (employee_id, first_name, last_name, department, salary) VALUES
(1, 'John', 'Doe', 'IT', 90000),
(2, 'Jane', 'Smith', 'HR', 85000),
(3, 'Mike', 'Johnson', 'IT', 82000),
(4, 'Sara', 'Williams', 'Sales', 77000),
(5, 'Tom', 'Brown', 'HR', 75000);

Numbering employees within departments

SELECT
employee_id,
first_name,
last_name,
department,
salary,
ROW_NUMBER() OVER (PARTITION BY department ORDER BY salary DESC) AS row_num
FROM
employees;

Result:

employee_idfirst_namelast_namedepartmentsalaryrow_num
1JohnDoeIT900001
3MikeJohnsonIT820002
2JaneSmithHR850001
5TomBrownHR750002
4SaraWilliamsSales770001
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