How to link database A in server X to database B in server Y?

hi all,

At the first, please let me say sorry for my poor english.

I have two postgresql database(A and B) running in different machines(X and
Y). I want to visit tables of B from A as if they are tables of A, could
you tell me how can I do?

For example, table t1 belongs to database A, which is located in server X;
             table t2 belongs to database B, which is located in server Y.

What I want is : do the below query in database A:
              select t1.field1,t2.field2
              from t1,t2
              where......

Is it possible?
If you have any idea, please let me know.
Thanks in advance.

Best regards,
Long

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