Lesson 4
Lesson learned: Try out transaction before committing it using begin tran keywords in T-SQL
Why transaction is about changing the db. you want to try out how it works before actually ding it
How to write " begin tran" before your command.
run including these words

1. you will see num of rows affected ( it can give you some hint)

2.you can work with modified version of db around 20 min

Note -the db becomes inaccessible to other users meanwhile

3.print and run "commit" to save the changes, "rollback" to undo

4.if nothing done ( in step 3) rollback is automatically done by system in like 20 minutes

How I learned
If I have nothing to do at work, I tell that to the teamlead and sit nearby and learn from her work :)