SQL & PL/SQL

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



i want to insert all the value of ZZ.VALU in XY.VALU.
The match value of ZZ.X and XY.X have the same value of ZZ.VALU

For example
X VALU
---------- ----

14 uvw
12 uvw

12 uvw

14 uvw


Here the field value of X 12 AND 14 are repeated but for two different record 12 have the same value in the field ZZ.VALU
Regards.