sql find unique records from 2 diff table

Question

my que is

how to find unique records from 2 diff table in diff database

for example

1st database   1sttable      2nddatabase 2nd table

               

      1st table has 14,15,16,17

      2nd table has 13,14,15,16,17,18

so i want only 13 and 18 record