What happens if you don't commit a transaction to a database (say, SQL Server)?

Question

Suppose I have a query:

begin tran
-- some other sql code

And then I forget to commit or roll back.

If another client tries to exec

Answer 1

Transactions are intended to run completely or not at all. The only way to complete a transaction is to commit, any other way will result in a rollback.

Therefore, if you begin and then not commit, it will be rolled back on connection close (as the transaction was broken off without marking as complete).