As you suggested, you index both MonkID and HobbyID because you're planning to search for all monks with a particular hobby and all the hobbies of a specific monk.

But that doesn't mean you won't want a single primary key rather than a composite one. The db theory book I've got here says "When possible we should try to avoid composite primary keys for entities..." although it isn't kind enough to offer a compelling reason, or really any reason at all. If you ever need to refer any of the tuples in the third table within another table, you'll probably want a single key.

But I seem to recall that you can use the internal tuple identification (in Postgres, at least, where I believe it is the oid) rather than a sequence for such cases. I can't access the postgres site currently, so I'm unable to verify that, and I don't know if that's possible or recommended with other databases.

In reply to RE(3): Indexing Sublists (kudra: composite primary keys--databases) by kudra
in thread Indexing Sublists by httptech

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.