This is just an explanation not addressed in other answers
At least in recent versions of Mysql, your first query is not committed.
If you query it under the same session you will see the changes, but if you query it from a different session, the changes are not there, they are not committed.
What's going on?
When you open a transaction, and a query inside it fails, the transaction keeps open, it does not commit nor rollback the changes.
So BE CAREFUL, any table/row that was locked with a previous query likeSELECT ... FOR SHARE/UPDATE, UPDATE, INSERT or any other locking-query, keeps locked until that session is killed (and executes a rollback), or until a subsequent query commits it explicitly (COMMIT) or implicitly, thus making the partial changes permanent (which might happen hours later, while the transaction was in a waiting state).
That's why the solution involves declaring handlers to immediately ROLLBACK when an error happens.
Extra
Inside the handler you can also re-raise the error using RESIGNAL, otherwise the stored procedure executes "Successfully"
BEGIN
DECLARE EXIT HANDLER FOR SQLEXCEPTION
BEGIN
ROLLBACK;
RESIGNAL;
END;
START TRANSACTION;
#.. Query 1 ..
#.. Query 2 ..
#.. Query 3 ..
COMMIT;
END