session begins

SET GLOBAL TRANSACTION

ISOLATION LEVEL SERIALIZABLE;

session ends

session begins

SET SESSION TRANSACTION

ISOLATION LEVEL READ UNCOMMITTED;

transaction $1$

transaction $2$

SET TRANSACTION

ISOLATION LEVEL REPEATABLE READ;

transaction $3$

transaction $4$

SET TRANSACTION

ISOLATION LEVEL READ COMMITTED;

transaction $5$

session ends

Select each transaction's isolation level.