It is used to permanently save any transaction into the database. Once you commit you can not rolled back the transaction.
Syntax:
COMMIT;
Note: Refer same post- BEGIN TRAN, ROLLBACK
Let’s understand with an example:
Step 1: Sample data as below:

SQL Sample Data
Step 2: Delete all records from Students Table using BEGIN TRAN command.
Query:
BEGIN TRAN T1 DELETE Students --T1 : is Transaction name --Execute both query together

BEGIN TRAN with Delete Statement
Step 3: All records has been deleted.
SELECT * FROM Students

Select Statement
Step 4: Here we used BEGIN TRAN before SQL Query statement, so it holds the transaction until the transaction is either committed or rolled back.
Step 5: Now Rolled back the transaction.
ROLLBACK TRAN T1

ROLLBACK TRAN
Step 6: check the table all records rolled back or not?
SELECT * FROM Students

SELECT Statement-2
Step 7: As you saw, all records rolled back successfully, now delete all records again and commit the transaction.
Query:
BEGIN TRAN T1 DELETE Students
Step 8: Now Commit the Transaction
COMMIT TRAN T1

COMMIT TRAN T1
Step 9: After commit, previous deleted transaction saved successfully, now try to ROLLBACK them.

Commit Transaction Example
As you saw, after Commit you can not rolled back any transactions. Now select Students table.

Select Record from table
As you saw, you can not rolled back them.
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