SQL Transaction Example

Transactions in SQL

In the process of this exercise, we observe how a given type of the table lock level interacts with the blocking that sets out the transaction at the query.
Select the table that contains the dictionary with the column names.

Write a query that will change the name in the directory row in the SQL window: convert ii from uppercase to lowercase and vice versa.

UPDATE Applications

SET AName = Upper(AName)

WHERE ID = 1


UPDATE Applications

SET AName = LOWER(AName)

WHERE ID = 1

Put this query in a transaction.

BEGIN TRANSACTION

    	UPDATE Applications 
SET AName = Upper(AName) 
WHERE ID = 1

UPDATE Applications 
SET AName = LOWER(AName) 
WHERE ID = 1

COMMIT TRANSACTION

Check the transactions available at the server using the system view sys.dm_tran_active_transactions in a new SQL window.

SELECT * FROM sys.dm_tran_active_transactions

Check the lock resources available on the server using the system view sys.dm_tran_locks in a new SQL window.

SELECT * FROM sys.dm_tran_locks 

Run the transaction opening, update, and display the table with SELECT statement, without a transaction completion. Make sure the update is reflected for the transaction.

BEGIN TRANSACTION

UPDATE Applications 
SET AName = Upper(AName) 
WHERE ID = 1

UPDATE Applications 
SET AName = LOWER(AName) 
WHERE ID = 1
	
SELECT * FROM Applications

1. Print the same table with the lock 7 in the new SQL window.
2. Missing(NOLOCK). Check the changes.
3. Row locks ROWLOCK or default (READCOMMITTED). Make sure the window goes into standby mode.

BEGIN TRANSACTION 
INSERT INTO Applications (ID, AName, AVersion) VALUES (4, 'Photoshop', 2015)
		WAITFOR DELAY '00:01'
ROLLBACK

SELECT * FROM Applications

SELECT * FROM Applications WITH (NOLOCK)

SELECT * FROM Applications WHERE ID = 2

SELECT * FROM Applications WHERE AName = 'Photoshop'

 

Check the transactions available at the server using the system view sys.dm_tran_active_transactions in the SQL window. You should see a new user transaction.

Check the locks on resources available on the server using system view sys.dm_tran_locks in the SQL window. The lock associated with active table should be added. Determine which resource is locked.

SELECT b.name, c.name, a.*
FROM sys.dm_tran_locks a
INNER JOIN sys.databases b ON a.resource_database_id = database_id
INNER JOIN sys.objects c ON a.resource_associated_entity_id = object_id

Roll back the transaction in the window — use only the ROLLBACK statement. The output of the table using SELECT statement should show the difference with the upgrade.

BEGIN TRANSACTION

UPDATE Applications 
SET AName = Upper(AName) 
WHERE ID = 3

UPDATE Applications 
SET AName = LOWER(AName) 
WHERE ID = 3

ROLLBACK TRANSACTION 

SELECT * FROM Applications

After re-output of the view, a user transaction in the SQL window should disappear.

SELECT * FROM sys.dm_tran_active_transactions 

After re-output of the view, a lock connected with the current table in the SQL window should disappear.

SELECT b.name, c.name, a.*
FROM sys.dm_tran_locks a
INNER JOIN sys.databases b ON a.resource_database_id = database_id
INNER JOIN sys.objects c ON a.resource_associated_entity_id = object_id

The contents of the table involved with the canceled update should finally appear in the SQL window.

Thanks for your attention!

 

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