FOREIGN KEY constraints in SQL Server

Server
There are 3 ways to establish foreign key constraints in SQL Server:
1.Enterprise Manager, Tables,design table, set the properties of the table,
can establish constraint, reference key;
2.Enterprise Manager, diagrams, new diagrams, establishes a two-table relationship.
3. Direct use of Transact SQL statements.

Three methods need to establish a data table first.
--Create TABLE Author:
CREATE TABLE [dbo]. [Author] (
[ID] [bigint] not NULL,
[AuthorName] [Char] (a) NULL,
[Address] [Char] () NULL,
[Introduction]  [ntext] Null
)

--Create TABLE Mybbs:
Reate TABLE [dbo]. [Mybbs] (
[ID] [bigint] IDENTITY (1, 1) is not NULL,
[Authorid] [bigint] Not NULL,
[Title] [Char] (a) NULL,
[Date_of_created] [DateTime] Null
[Abstract] [Char] () NULL,
[Content]  [ntext] Null
)

To set the Authorid in table Mybbs as a foreign key, use the Transact SQL statement directly, referring to the ID field of the author table, as follows:
--Adds a foreign key constraint to the table Mybbs (Authorid) Fk_mybbs_author, and Authorid in table Mybbs is constrained by the primary key ID in the table author:
BEGIN TRANSACTION
ALTER TABLE DBO.MYBBS add constraint Fk_mybbs_author
Foreign KEY (Authorid)
References Dbo.author ([id]) on UPDATE CASCADE on DELETE CASCADE

--Delete the foreign KEY constraint Fk_mybbs_author:
--alter table Dbo.mybbs drop constraint Fk_mybbs_author
--rollback
Commit TRANSACTION

The above on UPDATE cascade,on delete CASCADE Two options, indicating that the ID field of the author table after delete,update operation, the IDs in the Mybbs table are also deleted or updated. If unchecked, it is not possible to update or delete an ID that has been associated with the Mybbs table in the author table.