PL/SQL Update Join?

Question

I know there is no Update-Join statement in PL/SQL. I used to write T-SQL.

I have two tables.

Alex_Table1
---------------------------
PK         VAL
---------------------------
1          Value1
2          Value2
3          Value3


Alex_Table2
---------------------------
PK         VAL
---------------------------
1          Value1_2
3          Value3_2

I want to update VAL from Alex_Table2 to Alex_Table1 joining by PK column.

In T-SQL, that is simple

update t1 set t1.VAL = t2.VAL
from
    Alex_Table1 t1
    inner join Alex_Table2 t2 on t1.PK = t2.PK;

And the result is what I expected

Alex_Table1
---------------------------
PK         VAL
---------------------------
1          Value1_2
2          Value2
3          Value3_2

My question is how to do in PL/SQL? Thanks!

Update

Thanks Cybernate and ypercube gave me two useful solutions. They both work. However, I want to let you know the performance between these two statements.

My actual table contains 80,000 records and only 3,000 needs update.

MERGE statement takes 0.533 seconds.

UPDATE EXISTS statement takes over 3 minutes ( I did not measure the actual time. I terminated my process after 3 minutes.)

Answer 1

Use a MERGE statement:

MERGE INTO Alex_Table1 t1
USING Alex_Table2 t2
ON (t1.PK = t2.PK)
WHEN MATCHED THEN 
UPDATE SET t1.VAL = t2.VAL

Answer 2

UPDATE Alex_Table1 t1
SET t1.VAL =
      ( SELECT t2.VAL 
        FROM Alex_Table2 t2
        WHERE t2.PK = t1.PK
      )
WHERE EXISTS
        ( SELECT *
          FROM Alex_Table2 t2
          WHERE t2.PK = t1.PK
        )

This also works (as long as (PK) is the primary key of Alex_Table2):

UPDATE
  ( SELECT t1.VAL A, t2.VAL B
    FROM Alex_Table1 t1
      JOIN Alex_Table2 t2
        ON t2.PK = t1.PK
  )
SET A = B ;

Tested at dbfiddle.uk.