Generate Row Serial Numbers in SQL Query

select 
  ROW_NUMBER() Over (Order by CustomerID) As [S.N.], 
  CustomerID , 
  CustomerName, 
  Address, 
  City, 
  State, 
  ZipCode  
from Customers;

I'm not certain, based on your question if you want numbered rows that will remember their numbers even if the underlying data changes (and gives a different ordering), but if you just want numbered rows - that reset on a change in customer ID, then try using the Partition by clause of row_number()

row_number() over(partition by CustomerID order by CustomerID)

Sometime we might don't want to apply ordering on our result set to add serial number. But if we are going to use ROW_NUMBER() then we have to have a ORDER BY clause. So, for that we can simply apply a tricks to avoid any ordering on the result set.

SELECT ROW_NUMBER() OVER(ORDER BY (SELECT 1)) AS ItemNo, ItemName FROM ItemMastetr

For that we don't need to apply order by on our result set. We'll just add ItemNo on our given result set.

Implementing Serial Numbers Without Ordering Any of the Columns

Demo SQL Script-

IF OBJECT_ID('Tempdb..#TestTable') IS NOT NULL
    DROP TABLE #TestTable;

CREATE TABLE #TestTable (Names VARCHAR(75), Random_No INT); 

INSERT INTO #TestTable (Names,Random_No) VALUES
 ('Animal', 363)
,('Bat', 847)
,('Cat', 655)
,('Duet', 356)
,('Eagle', 136)
,('Frog', 784)
,('Ginger', 690); 

SELECT * FROM #TestTable;

There are ‘N’ methods for implementing Serial Numbers in SQL Server. Hereby, We have mentioned the Simple Row_Number Function to generate Serial Numbers.

ROW_NUMBER() Function is one of the Window Functions that numbers all rows sequentially (for example 1, 2, 3, …) It is a temporary value that will be calculated when the query is run. It must have an OVER Clause with ORDER BY. So, we cannot able to omit Order By Clause Simply. But we can use like below-

SQL Script

IF OBJECT_ID('Tempdb..#TestTable') IS NOT NULL
    DROP TABLE #TestTable;

CREATE TABLE #TestTable (Names VARCHAR(75), Random_No INT); 

INSERT INTO #TestTable (Names,Random_No) VALUES
 ('Animal', 363)
,('Bat', 847)
,('Cat', 655)
,('Duet', 356)
,('Eagle', 136)
,('Frog', 784)
,('Ginger', 690); 

SELECT Names,Random_No,ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS SERIAL_NO FROM #TestTable;

In the Above Query, We can Also Use SELECT 1, SELECT ‘ABC’, SELECT ” Instead of SELECT NULL. The result would be Same.