SQL & PL/SQL :: Update Table From Other Table?

i want to update one table form an other table, for example

SQL> select * from zz;

X VALU
---------- ----
25 abc
18 xyz
14 uvw
12 uvw
26 abc
12 uvw
30 asdf
14 uvw
22 kmn

SQL> select * from xy;

X
----------
12
14
18
22
14
30
25
12
26

9 rows selected

we have two table ZZ AND XY (There is no primary key constraint on these table), ZZ contain two field i.e "X" and "VALU" and XY contain only one field i.e is X. In table ZZ and XY the field X have the same value but not in the same sequence and X have also the duplicated value in both table. now i Add new column in Table XY i.e Valu

SQL> alter table xy
2 add (valu varchar2(6))
3 ;

Table altered.

SQL> select * from xy;

X VALU
---------- ------
12
14
18
22
14
30
25
12
26

9 rows selected. now i want to update the table XY from the table ZZ and set the "valu" in such a manner that the value of field ZZ.Valu insert in the table XY. and it final display the result i.e.
X VALU
---------- ------
12 uvw
14 uvw
18 xyz
22 kmn
14 uvw
30 asdf
25 abc
12 uvw
26 abc