Select dates that match from same table.

Question

I wish to update a selection of records
where the order_date is the same, and the customer_id is the same.
The update simply need to be to change the order date on both to the lowest date of the two(or how ever many there are for that date).
e.g.
Ship_date / Order_date / customer_id
1-02-01 2-01-01 1
1-02-01 12-01-01 1
12-01-01 1-01-01 2
12-01-01 5-01-01 2
## So above the first 2 records would have the order_date set to the lowest date of the two records.
A self join ?
Not really sure about this, Thanks in advance!

Answer 1

You could try this (not tested):
UPDATE yourTable t1
SET t1.Order_Date = (SELECT min(t2.Order_date)
                           FROM yourTable t2
                           WHERE t2.ship_date = t1.ship_date
                           AND t2.customer_id = t1.customer_id)However this also updates columns that already have the minimum value. Maybe you would like to avoid it, then add some where clause to the Update statement.
Changed because order_date and ship_date needed to be switched.
Message was edited by:
Sven Weller