Question

To assist in understanding I have a table like this:

itemcode itemname icode serialnum
1        A        10    0
2        B        10    0
3        C        10    0
4        D        11    0
5        E        13    0
6        F        20    0
7        G        20    0

I want the result to look like the table below using a single update query with the help of looping cursors:

itemcode itemname icode serialnum
1        A        10    1
2        B        10    2
3        C        10    3
4        D        11    1
5        E        13    1
6        F        20    1
7        G        20    2

Item code is the primary key in this table. The logic behind generating the serial number is whenever icode changes the serial number gets reset to 1. I need a single update query to update the table with the help of cursors if someone can assist with a solution?

Answer 1

So you want a sequential serial number for every icode-group. Then you can use ROW_NUMBER with PARTITION BY icode:

WITH CTE AS
(
  SELECT itemcode, itemname, icode, serialnum,
     ,   ROW_NUMBER() OVER (PARTITION BY icode ORDER BY itemcode) AS RN
  FROM dbo.TableName 
)
UPDATE CTE SET serialnum = RN;

If you want it to be reculculated on every update you could use a trigger:

CREATE TRIGGER dbo.TableName_Updated
ON dbo.TableName 
FOR UPDATE /* Fire this trigger when one or multiple rows are UPDATEd */
AS BEGIN
    WITH CTE AS
    (
      SELECT itemcode, itemname, icode, serialnum,
         ,   ROW_NUMBER() OVER (PARTITION BY icode ORDER BY itemcode) AS RN
      FROM dbo.TableName t INNER JOIN INSERTED i 
        ON t.itemcode = i.itemcode
    )
    UPDATE CTE SET serialnum = RN
END