If the columns and names are the same then, as earlier suggest,  insert into foo select * from bar will work fine.

Depending on your RDBMS and how things are setup you may be able to specify a table in a different database as database:bar or some such, but this can run into problems with transactions etc.

If you're doing bulk copies, it's probably faster to:

• dump table contents into text files
• turn off logging on target database
• load text files into target database tables (sqlloader for oracle, load for informix etc)

Depending on volume of course...