sql server - Trigger that doesn't allow you to introduce data if it already exists in a table

Question

I'm a newbie when it comes to SQL Server and I have a problem creating a trigger.

I have a table called Concert and I have to create a trigger (I think?) that doesn't allow adding concerts to the database if there are already shows planned on the date that I am choosing, in the concert hall that I am choosing.

Something like

• if hall and date combination already exists in table => trigger ('not allowed')

This is my (very bad attempt):

CREATE TRIGGER unavailable_show
ON Concert
FOR INSERT
AS
BEGIN
    IF EXISTS (SELECT Date, HallID FROM INSERTED)  
    ROLLBACK TRANSACTION
END

Answer 1

等待大神答复