Trigger to update foreign key field after insert on same table - sql

Question

I have two tables:
Table1 (surveyid [PKID], surveyname)
Table2 (visitid [PKID], surveyname, surveyid [FKID - refers to Table1]).
After inserting a new row into Table2, I would like to update Table2.surveyid with the surveyid from Table1, based on matching surveyname.
I thought it maybe wasn't possible (or good practice?) to create a trigger to update the same table. But I seem to have created a trigger that will do this. The problem is that after insert, the trigger updates the surveyid for every row, instead of just the newly inserted rows.
This trigger code works, but how do I ensure the trigger only updates the surveyid for newly inserted rows, and not all rows?
CREATE TRIGGER tr_update_table2_fk
ON Table2
AFTER INSERT
AS
BEGIN
UPDATE Table2
SET surveyid = (SELECT t1.surveyid
FROM Table1 t1
WHERE t1.surveyname = Table2.surveyname)
END;

Answer 1

Thank you MattM and DaleK, you've helped me figure out the answer. I was adding the inserted table into the subquery where clause before, instead of the query where clause. This does the trick:
CREATE TRIGGER tr_update_table2_fk
on Table2
AFTER INSERT
AS
BEGIN
UPDATE Table2 SET
surveyid = (
SELECT t1.surveyid
FROM Table1 t1
WHERE t1.surveyname = Table2.surveyname
)
WHERE Table2.visitid IN (SELECT visitid FROM inserted)
END;

Answer 2

Yes, the inserted table is the answer.
I'd use it to capture the visitids of the inserted rows, then filter by them in a WHERE clause on the end of your UPDATE statement in your trigger.
E.g.
CREATE OR ALTER TRIGGER tr_update_table2_fk
ON Table2
AFTER INSERT
AS
BEGIN
DROP TABLE IF EXISTS #VisitIds ;
CREATE TABLE #VisitIds ( [id] INT ) ;
INSERT INTO #VisitIds ( [id] )
SELECT [visitid]
FROM inserted ;
UPDATE Table2
SET [surveyid] =
(
SELECT t1.[surveyid]
FROM Table1 AS t1
WHERE t1.[surveyname] = Table2.[surveyname]
)
WHERE [visitid] IN ( SELECT [id] FROM #VisitIds ) ;
END
GO