Merge 2 pairs of tables from 2 databases. Beginner
how about?

create table DB3.tbl1 as
select * from (
  select
    DB1.tbl1.Col1,
    DB1.tbl1.Col2, ...
    DB1.tbl1.ColZ
  from DB1.tbl1
  union all
  select
    DB2.tbl1.Col1 + n
    DB2.tbl1.Col2, ...
    DB2.tbl1.ColZ
  from DB2.tbl1
)


could also replace the + n by + ( select count(*) from DB1.tbl1 )