This article will explain how we can add sequence row number to a SQL select query starting from 1 onwards. This can be achieved by using built in SQL function ROW_NUMBER(). This function simply generates row number for each row in the result. You can specify the partition and order by criteria. This is how it works:
e.g. Suppose we have a table Employees.
SELECT EmployeeId, EmployeeName, Salary FROM Employees
EmployeeId EmployeeName Salary
-------------------------------------
1002 Alden 4000
2343 Lawson 4500
2004 Barbra 4800
1105 Marsden 4500
3116 Mac 5000
Use of ROW_NUMBER() will assign sequence number to rows as:
SELECT ROW_NUMBER()
OVER (ORDER BY EmployeeName) AS Row,
EmployeeId, EmployeeName, Salary
FROM Employees
Row EmployeeId EmployeeName Salary
-------------------------------------------
1 1002 Alden 4000
2 2343 Lawson 4500
3 2004 Barbra 4800
4 1105 Marsden 4500
5 3116 Mac 5000
Using ROW_NUMBER() for calculating Nth highest salary
We can utilize this function for calculating Nth highest salary of a employee. Suppose we want to find employee with 4th highest salary. This can be done as:
SELECT * FROM
(SELECT ROW_NUMBER()
OVER (ORDER BY Salary) AS Row,
EmployeeId, EmployeeName, Salary
FROM Employees) AS EMP
WHERE Row = 4
Row EmployeeId EmployeeName Salary
-------------------------------------------
4 1105 Marsden 4500
Using ROW_NUMBER() in case of pagination
This can also be used for getting rows which belongs to a particular page only. This is very common scenario of a business application where we have lots of rows in database and we want to filter based on page number.
SELECT * FROM
(SELECT ROW_NUMBER()
OVER (ORDER BY EmployeeName) AS Row,
EmployeeId, EmployeeName, Salary
FROM Employees) AS EMP
WHERE Row BETWEEN 2 AND 4
Row EmployeeId EmployeeName Salary
-------------------------------------------
2 2343 Lawson 4500
3 2004 Barbra 4800
4 1105 Marsden 4500