Is there any simple way to merge two tables in different formats in two databases?

two programs merge, each has its own database, want to merge this piece together, do not intend to change the code, this will change bigger, there is no simple way to directly modify the database, I intend to first merge the database, such as table An and table B, called table An after the merger, but I do not intend to change the code of B, can you add some code in the database, similar to aliases and so on. For example, the program of B automatically goes to Table A when it calls Table B. Of course, I need to unify the format of Table An and Table B. this is easy.
I checked postgresql"s command, and there are some names that are only temporary. Should not be able to meet my needs.

Mar.04,2021

you can consider using views

https://www.postgresql.org/do.

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b32931-2ab6c.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b32931-2ab6c.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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