Triggering an Update a value after Insert and Delete operations? - sql

Question

I have an activity from my SQL Server class and I'm missing only this trigger to complete it.
My teacher has asked in this activity to do the following trigger operation on a column sequential on telefone table.
After an insert statement, always keep the values in sequence like the first record is 0, the next should be 1 and there it goes.
And for the delete statement if someone removes a record the sequential value should be reordered.
I've got the insert statement working fine creating a sequence and adding it's next value to the column.
But no lucky with the delete statement.
Here's what I have so far for the trigger:
CREATE TRIGGER tg_sequencial
ON Telefone
AFTER INSERT, UPDATE
AS
BEGIN
DECLARE #vSequencial_Ins INT, #vSequencial_Del INT
SELECT #vSequencial_Ins = inserted.Sequencial FROM inserted
SELECT #vSequencial_Del = deleted.Sequencial FROM deleted
-- Check if it is an insert operation
if(#vSequencial_Ins IS NOT NULL AND #vSequencial_Del IS NULL)
begin
update Telefone set Sequencial = NEXT VALUE FOR dbo.Sequencial
from Telefone tel
join inserted i on i.IdPessoa = tel.IdPessoa
end
-- Check if it is an delete operation
else if(#vSequencial_Ins IS NULL AND #vSequencial_Del IS NOT NULL)
begin
alter sequence dbo.Sequencial
restart with 0
end
end
And this is the sequence code:
CREATE SEQUENCE dbo.Sequencial
START WITH 0
INCREMENT BY 1
NO CACHE
;
GO
My telefone table has the following values:
Sequencial smallint not null [PK]
IdPessoa int not null[PFK],
IdTipoTelefone tinyint not null [FK],
NumeroTelefone int not null,
DDD tinyint not null
EDIT: Got insert trigger working fine after changing the code from:
update Telefone set Sequencial = NEXT VALUE FOR dbo.Sequencial
To:
update Telefone set Sequencial = NEXT VALUE FOR dbo.Sequencial
from Telefone tel
join inserted i on i.IdPessoa = tel.IdPessoa
It now affects just the selected row instead of increasing all the fields.