when/what locks are hold/released in READ COMMITTED isolation level

Question

I am trying to understand isolation/locks in SQL Server.

I have following scenario in READ COMMITTED isolation level(Default)

We have a table.

Answer 1

First, lock only acquire when statement run. Your statement seprate in two pieces, suppose to be simplfy:

select * from Transactions
update Transactions set amt = xxx where Tid = xxx

When/what locks are hold/released in READ COMMITTED isolation level? when select * from Transactions run, no lock acquired.

Following update Transactions set amt = xxx where Tid = xxx will add X lock for updating/updated keys, IX lock for page/tab

All lock will release only after committed/rollbacked. That means no lock will release in trans running.