How to simulate DEADLOCK on SQL Server?

You can create a deadlock by using the steps shown below. First, create the global temp tables with sample data.

--Two global temp tables with sample data for demo purposes.
CREATE TABLE ##Employees (
    EmpId INT IDENTITY,
    EmpName VARCHAR(16),
    Phone VARCHAR(16)
)
GO

INSERT INTO ##Employees (EmpName, Phone)
VALUES ('Martha', '800-555-1212'), ('Jimmy', '619-555-8080')
GO

CREATE TABLE ##Suppliers(
    SupplierId INT IDENTITY,
    SupplierName VARCHAR(64),
    Fax VARCHAR(16)
)
GO

INSERT INTO ##Suppliers (SupplierName, Fax)
VALUES ('Acme', '877-555-6060'), ('Rockwell', '800-257-1234')
GO

Now open two empty query windows in SSMS. Place the code for session 1 in one query window and the code for session 2 in the other query window. Then execute each of the two sessions step by step, going back and forth between the two query windows as required. Note that each transaction has a lock on a resource that the other transaction is also requesting a lock on.

Session 1                   | Session 2
===========================================================
BEGIN TRAN;                 | BEGIN TRAN;
===========================================================
UPDATE ##Employees
SET EmpName = 'Mary'
WHERE EmpId = 1
===========================================================
                             | UPDATE ##Suppliers
                             | SET Fax = N'555-1212'
                             | WHERE SupplierId = 1
===========================================================
UPDATE ##Suppliers
SET Fax = N'555-1212'
WHERE SupplierId = 1
===========================================================
<blocked>                    | UPDATE ##Employees
                             | SET Phone = N'555-9999'
                             | WHERE EmpId = 1
===========================================================
                             | <blocked>
===========================================================

A deadlock results; one transaction finishes and the other transaction is aborted and error message 1205 is sent to client.

Close the SSMS query windows for "Session 1" and "Session 2" to commit (or rollback) any open transactions. Lastly, cleanup the temp tables:

DROP TABLE ##Employees
GO
DROP TABLE ##Suppliers
GO