Purpose

This repostiory contains examples which might be used to show/explain why and when deadlocks happen in MSSQL.

How to

1. Open two different SQL sessions.
2. In each session open one file.
3. Run SQL commands according to comments.

For example - running Read Commited should look like:

Session 1

SET TRANSACTION ISOLATION LEVEL READ COMMITTED;

BEGIN TRANSACTION
    UPDATE Wycieczki
        SET cena = cena*2
    WHERE
        kraj = 'Bangkok'
-- STEP 1 RUN ABOVE

Session 2

SET TRANSACTION ISOLATION LEVEL READ COMMITTED;

BEGIN TRANSACTION
    UPDATE Bilety
        SET cena = cena * 2
    WHERE
        kraj = 'Ateny'
-- STEP 2 - RUN ABOVE

Session 1

    SELECT
        *
    FROM
        Bilety
    WHERE
        kraj = 'Ateny'
-- STEP 3 RUN BETWEEN 1 AND 3
COMMIT TRANSACTION -- COMMIT AFTER DEADLOCK HAPPENS

Session 2

    SELECT
        *
    FROM
        Wycieczki 
    WHERE
        kraj = 'Bangkok'
-- STEP 4 RUN BETWEEN 2 AND 4
COMMIT TRANSACTION -- COMMIT AFTER DEADLOCK HAPPENS