Update table after delete using trigger - sql

Question

As the title states, I'm trying to use a trigger to update a value in Table2 when a row gets deleted from Table1. My code looks like this:
CREATE TRIGGER TRG_Table1_DEL
ON Table1
FOR DELETE
AS
UPDATE Table2 SET
FK_Table1ID = NULL
WHERE FK_Table1ID = (SELECT Table1ID FROM DELETED)
The first error I get is with the UPDATE command and that states:
"Incorrect syntax near 'UPDATE'. Expecting EXTERNAL.
The second error
is with the DELETED table that I'm trying to access. This states
"Invalid object name 'DELETED'.
Overall, I'm just trying to mimic a constraint that sets the column to null (ON DELETE SET NULL). I'm doing this because I got an error saying I might cause multiple cycles or cascade paths when trying to add the constraint.
For my code, I based it off this answer.

Answer 1

This should work in SQL Server. I have just replaced (=) with (in).
CREATE TRIGGER TRG_Table1_DEL
ON Table1
FOR DELETE
AS
UPDATE Table2
SET FK_Table1ID = NULL
WHERE FK_Table1ID IN (SELECT Table1ID FROM DELETED)
Example:
create table empsalary(empid int, month int , salary int);
insert into empsalary values(1, 1, 100);
insert into empsalary values(1, 2, 101);
insert into empsalary values(1, 3, 103);
create table emp(empid int, id int);
insert into emp values(1,1);
CREATE TRIGGER TRG_Table1_DEL
ON empsalary
FOR DELETE
AS
UPDATE emp
SET id = NULL
WHERE empid IN (SELECT empid FROM DELETED)
select * from empsalary
empid
month
salary
1
1
100
1
2
101
1
3
103
select * from emp
empid
id
1
1
delete empsalary where month=1;
select * from empsalary;
empid
month
salary
1
2
101
1
3
103
select *from emp;
empid
id
1
null
db<>fiddle here

Answer 2

The problem turned out to have a very simple fix. I was getting the errors because I was trying to add the trigger after dropping a constraint. This is fine, but I forgot to add a GO command in between the dropping of the constraint and the creation of the trigger. My code looked like this:
DROP CONSTRAINT
ADD TRIGGER
but this was the correct solution:
DROP CONSTRAINT
GO
ADD TRIGGER
Edit: as DaleK has pointed out, I also need to modify the WHERE clause in case the DELETED table has multiple rows