Sorry for being slow getting back, I have been offline.

The answer is that the database is supposed to figure out exactly what the SQL is supposed to do, and then come up with a very efficient way to do that. With a Turing-complete language it is impossible to answer detailed questions about arbitrary code, and is difficult to answer them even for normal code.

Sure, optimizers can speed up code. But in a normal language they can't recognize a bad algorithm and rewrite it with a more efficient one. But SQL routinely is optimized to be using algorithms which are far better than any that the developer would have thought up.

SQL could not do this if the developer had, for instance, the freedom to write a series of nested loops with possibly relevant side-effects and a difficult to discern purpose.

In reply to Re: Re: Re (tilly) 4: How NOT to do it by tilly
in thread How NOT to do it by jlawrenc

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.