i have two tables
Order(id, date, note)
and
Delivery(Id, Note, Date)
I want to create a trigger that updates the date in Delivery when the date is updated in Order.
I was thinking to do something like
CREATE OR REPLACE TRIGGER your_trigger_name
BEFORE UPDATE
ON Order
DECLARE
BEGIN
UPDATE Delivery set date = ??? where id = ???
END;
How do I get the date and row id?
thanks
In such a case, you can use the following UPDATE statement syntax to update column from one table, based on value of another table. UPDATE first_table, second_table SET first_table. column1 = second_table. column2 WHERE first_table.id = second_table.
In SQL Server, you can create DML triggers that execute code only when a specific column is updated. The trigger still fires, but you can test whether or not a specific column was updated, and then run code only if that column was updated. You can do this by using the UPDATE() function inside your trigger.
UPDATE table SET col = new_value WHERE col = old_value AND other_col = some_other_value; UPDATE table SET col = new_value WHERE col = old_value OR other_col = some_other_value; As you can see, you can expand the WHERE clause as much as you'd like in order to filter down the rows for updating to what you need.
How do i get the date and row id?
Assuming these are columns on your ORDER table called DELIVERY_DATE and ID your trigger should look something like this:
CREATE OR REPLACE TRIGGER your_trigger_name
BEFORE UPDATE ON Order
FOR EACH ROW
BEGIN
if :new.delivery_date != :old.delivery_date
then
UPDATE Delivery d
set d.delivery_date = :new.delivery_date
where d.order_id = :new.id;
end if;
END;
Note the FOR EACH ROW clause: that is necessary to reference values from individual rows. I have used an IF construct to test whether to execute the UPDATE on Delivery. If you have no other logic in your trigger you could write it like this...
CREATE OR REPLACE TRIGGER your_trigger_name
BEFORE UPDATE OF delivery_date ON Order
FOR EACH ROW
BEGIN
UPDATE Delivery d
set d.delivery_date = :new.delivery_date
where d.order_id = :new.id;
END;
I have answered the question you asked but, as an aside, I will point out that your data model is sub-optimal. A properly normalized design would hold DELIVERY_DATE on only one table: DELIVERY seems teh logical place for it.
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