MySQL InnoDB foreign key between different databases
I do not see any limitation on https://dev.mysql.com/doc/refman/8.0/en/create-table-foreign-keys.html.
So just use otherdb.othertable and you will be good.
It's possible : Link to do it
Example (Table1 is in database1 and HelloTable is in database2) :
ALTER TABLE Table1 ADD foreign key FK_table1(ColumnNameFromTable1)REFERENCES db2.HelloTable(ColumnNameFromHelloTable)
Below is how to add a foreign key on table t2, reference from table db1.historial(codh):
alter table t2add foreign key FK_t2(micod2) references db1.historial(codh) on delete cascade on update cascade;