I made a mistake in my advice. I use just "union" for small examples done
by hand, but when doing it for programattically generated SQL you want
to use "union all". "union all" doesn't remove duplicates and doesn't
waste effort checking for duplicates. So you really want something like:
INSERT INTO table ( col1, col2, col3 )
select value1, value2, value3 union all
select value4, value5, value6 union all
select value7, value8, value9;