Question

I am trying to write a trigger on a table to avoid insertion of two Names which are not flagged as IsDeleted. But the first part of selection contains the inserted one and so the condition is always true. I though that using FOR keyword causes the trigger to run before the INSERTION but in this case the inserted row is already in the table. Am I wrong or this is how all FOR trigger work?

ALTER TRIGGER TriggerName
ON MyTable
FOR INSERT, UPDATE
AS
BEGIN 
    If exist (select [Name] From MyTable WHERE IsDeleted = 0 AND [Name] in (SELECT [Name] FROM INSERTED)
    BEGIN
    RAISERROR ('ERROR Description', 16, 1);
    Rollback;
    END  
END

Answer 1

FOR runs after the data is changed, INSTEAD OF is what I think you are after.

EDIT: As stated by others, INSTEAD OF runs instead of the data you are changing, therefore you need to insert the data if it is valid, rather than stopping the insert if it is invalid.

Read this question for a much more detailed explanation of the types of Triggers.

SQL Server "AFTER INSERT" trigger doesn't see the just-inserted row