MySQL is an incredibly frustrating database when it comes to joins.. for whatever reason it seems to crawl to a halt when it comes to putting two tables together. So, in general, writing two seperate queries with Perl logic in between is often faster.

I wrote a reporting application that would join several million-row tables with complex WHERE clauses that returned back in, generally, under a second. Maybe your schema isn't designed with speed in mind?

Because you are doing a SELECT MIN() operation it is almost a guarantee that you cannot write this as a single query.

No. First, the inner query doesn't refer back to the outer query, so it's actually a constant that can be factored out. Second, every subquery can be rewritten as a join. Granted, you might have to do some funky HAVING and GROUP BY stuff, but it's possible.

My criteria for good software:
  1. Does it work?
  2. Can someone else come in, make a change, and be reasonably certain no bugs were introduced?

In reply to Re^2: Query rewriting question by dragonchild
in thread Query rewriting question by Anonymous Monk

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.