Need help regarding updating one table from another

[gandolf989]

Of course we know that the WHERE clause in the query is being applied to the update statement when we change the WHERE clause to WHERE 1=1 and get an error.

SQL> UPDATE t1
   SET val =
     ( SELECT val
         FROM t2
        WHERE 1=1 );
  2    3    4    5       ( SELECT val
       *
ERROR at line 3:
ORA-01427: single-row subquery returns more than one row