Auto-increment the value only when the value of another column changes sql server

Question

Let's say I have this (SQL server) database, sorted by value A and value B should be incremented only when the value A gets change:

BillNo Value B
SC-P1100 1
SC-P1100 1 BillNo changes
SC-blb00 2 BillNo changes
SC-P6010 3
SC-P6010 3
SC-P6010 3 BillNo changes
SB-T1810 4

How do I select the rows in the above manner? Please answer

Thanks

Answer 1

You can do it like this

UPDATE tableA   
  SET BillNo='new value'
  , ValueB=ValueB+1
  WHERE BillNo='Old value';

Answer 2

You can use CTE to do that.

WITH CTE (Col1, RowNumber)
AS
(
    SELECT <YOUR_COLUMN_NAME_HERE> AS Col1, ROW_NUMBER() OVER (ORDER BY Col1) As RowNumber
    FROM <YOUR_TABLE_NAME_HERE>
)

SELECT Col1, 
(
    SELECT COUNT(DISTINCT Col1)
    FROM CTE InnerCTE
    WHERE InnerCTE.RowNumber <= OuterCTE.RowNumber
) As NumberOfDistinctItemsInCol1
FROM CTE OuterCTE

Be sure to replace <YOUR_COLUMN_NAME_HERE> with your actual column name and <YOUR_TABLE_NAME_HERE> with your actual table name.