How can i implement a Slowly changing Dimension using the Query

Question

I have a historical table with data as bellow :

In my case the product id (110,111,112) had changed the price that way i have the same product with the value of the product_updateDate also sometimes i can have the same duplicate data with no information changed

+------+------------+--------------+---------------+-----------------------------+-------------------------+-------------------------+----------------+
| id   | product_id | product_name | product_Price |       product_addDate       |   product_UpdateDate    |      Insertdate_DB      | Updatedate_DB  |
+------+------------+--------------+---------------+-----------------------------+-------------------------+-------------------------+----------------+
|    1 |        110 |    DELL      |          1000 |    2017-03-01 08:00:00.000  | NULL                    | 2017-03-06 10:00:00.000 | NULL           |
|    2 |        111 |    HP        |           900 |    2017-03-01 08:00:00.000  | NULL                    | 2017-03-06 10:00:00.000 | NULL           |
| 3    |        112 |    Mac       |          1300 |    2017-03-01 08:00:00.000  | NULL                    | 2017-03-06 10:00:00.000 | NULL           |
| 4    |        113 |   Lenovo     |           950 |    2017-03-01 08:00:00.000  | NULL                    | 2017-03-06 10:00:00.000 | NULL           |
| 5    |        110 |   DELL       |           900 |    2017-03-04 08:00:00.000  | 2017-03-04 08:00:00.000 | 2017-03-07 10:00:00.000 | NULL           |
| 6    |        111 |    HP        |           800 |    2017-03-04 08:00:00.000  | 2017-03-04 08:00:00.000 | 2017-03-07 10:00:00.000 | NULL           |
| 7    |        112 |    Mac       |           120 |    2017-03-04 08:00:00.000  | 2017-03-04 08:00:00.000 | 2017-03-07 10:00:00.000 | NULL           |
+------+------------+--------------+---------------+-----------------------------+-------------------------+-------------------------+----------------+

What i want is doing an Update Query to get the result as bellow:

 +----+------------+--------------+---------------+-------------------------+-------------------------+-------------------------+---------------+
| id | product_id | product_name | product_Price |     product_addDate     |   product_UpdateDate    |      Insertdate_DB      | Updatedate_DB |
+----+------------+--------------+---------------+-------------------------+-------------------------+-------------------------+---------------+
|  1 |        110 | DELL         |          1000 | 2017-03-01 08:00:00.000 | 2017-03-04 08:00:00.000 | 2017-03-06 10:00:00.000 | GETDATE()     |
|  2 |        111 | HP           |           900 | 2017-03-01 08:00:00.000 | 2017-03-04 08:00:00.000 | 2017-03-06 10:00:00.000 | GETDATE()     |
|  3 |        112 | Mac          |          1300 | 2017-03-01 08:00:00.000 | 2017-03-04 08:00:00.000 | 2017-03-06 10:00:00.000 | GETDATE()     |
|  4 |        113 | Lenovo       |           950 | 2017-03-01 08:00:00.000 | NULL                    | 2017-03-06 10:00:00.000 | NULL          |
|  5 |        110 | DELL         |           900 | 2017-03-04 08:00:00.000 | NULL                    | 2017-03-07 10:00:00.000 | NULL          |
|  6 |        111 | HP           |           800 | 2017-03-04 08:00:00.000 | NULL                    | 2017-03-07 10:00:00.000 | NULL          |
|  7 |        112 | Mac          |           120 | 2017-03-04 08:00:00.000 | NULL                    | 2017-03-07 10:00:00.000 | NULL          |
+----+------------+--------------+---------------+-------------------------+-------------------------+-------------------------+---------------+

The query as bellow can update the product_UpdateDate

update tablename set product_UpdateDate=
case when tablename.product_UpdateDate is null then t.product_UpdateDate
else null end
from tablename 
join tablename t on tablename.product_id=t.product_id
and t.ID<>tablename.id `

But also i want to change the Updatedate_DB with the GETDATE() value when i try to do update this column all rows have the value GETDATE() but i want change only the rows that the value have change

Thanks for help

Answer 1

I am not sure I understood your question, but if you want to change only the row where you wrote a date (and not null), may be you could add this to your update:

, UPDATEDATE_DB=CASE WHEN TABLENAME.PRODUCT_UPDATEDATE IS NULL THEN 'GETDATE()'
ELSE TABLENAME.UPDATEDATE_DB END