One of the newest MySQL features as of MySQL 4.0 is the support for SQL unions. A union is simply a tool for combining the results from multiple selects into a single result set listing. A MySQL union looks like this:
SELECT first_name, last_name FROM Author UNION SELECT fname, lname FROM Editor;
This query will provide a list of all authors and editors in the
database. The list will include in the first column the values of the
first_name
column for authors and the values of
the fname
column for editors. The second column
will include the last_name
values for authors and
lname
values for editors.
If one person is an author and an editor, he will appear a single
time in the list. You can, however, get MySQL to show the person
twice in the results by using the
ALL
keyword:
SELECT first_name, last_name FROM Author UNION ALL SELECT fname, lname FROM Editor;