SQL Server trigger validation to insert or update - sql

Question

I have to develop a trigger for multiple value update for the Change_Table that contains two columns Article_C (primary key) and Status_C. The trigger activates when the Status_C column is updated and it needs to either insert or update the Target_Tablewhich columns are Article_T (primary key) and Status_T.
The Status column for both tables is a NOT NULL int
For insert validation: insert all Change_Table values (Articles & Status) that do not exist into the Target_Table.
For update condition: if the articles exist in the Target_Table, pass the updated status value to that table.
Status values are 1 or 2.
My current implementation:
CREATE TRIGGER [dbo].[Article_Trigger]
ON [dbo].[Change_Table]
AFTER UPDATE
NOT FOR REPLICATION
AS
IF UPDATE (Status_C)
BEGIN
INSERT INTO Target_Table (Article_T, Status_T)
SELECT Article_C, Status_C
FROM Change_Table
WHERE NOT EXISTS (SELECT * FROM Target_Table
WHERE Change_Table.Article_C = Target_Table.Article_T
AND Change_Table.Status_C = Target_Table.Status_T)
END
This is a rough idea of the insert but it only works once when the Change_Table is first updated and the target table is empty. After that I get an error "Violation of PRIMARY KEY constraint" due to duplicate primary key after updating the status for a second time due to the insert condition.
Query that gave error after second execution:
update Change_Table set status_c = 1 where Article_C in (1000,1003)
How can I modify this query to implement the update status condition to this trigger?

Answer 1

I think you could use deleted or inserted tables. These 2 virtual tables are working nicely with trigger. In you example, you may not need deleted table as you are not logging the historical changes.
CREATE TRIGGER [dbo].[Article_Trigger]
ON [dbo].[Change_Table]
AFTER UPDATE
NOT FOR REPLICATION
AS
IF UPDATE (Status_C)
BEGIN
--insert if not exist
INSERT INTO Target_Table
SELECT A.Article_C, A.Status_C
FROM inserted as A --the updated records from the source table will exist in the inserted virtual table
LEFT JOIN Target_Table as B
ON B.Article_T = A.Article_C
WHERE B.Article_T IS NULL
--update if exist
UPDATE A
SET A.Status_T = B.Article_C
FROM Target_Table as A
INNER JOIN inserted as B --the updated records from the source table will exist in the inserted virtual table
ON B.Article_C = A.Article_T
END