Beefy Boxes and Bandwidth Generously Provided by pair Networks
Just another Perl shrine
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??
Useful comment. I hadn't thought of getting SQL to do the logic.

An index on the columns in where clause might have a huge impact if you use count(*).

I believe that MySQL creates an index on the leftmost subset of columns anyway, due to the way it stores the data. It should be intelligent enough to only compare the second row if the first row succeeds. In the test case, only there are only 4 rows, so testing the remainder of the AND should be quick.

Have just tested the suggestion. In fact, not having indexes doesn't seem to make any difference (1230/sec vs. 1174/sec), so I think I am correct that there is an index by default on the leftmost column.
--
Brovnik


In reply to Re: Re: How to count rows using DBI & mysql - Performance results by Brovnik
in thread How to count rows using DBI & mysql - Performance results by Brovnik

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!
  • 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, 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, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • Outside of code tags, you may need to use entities for some characters:
            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.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others making s'mores by the fire in the courtyard of the Monastery: (3)
    As of 2014-09-22 02:48 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      How do you remember the number of days in each month?











      Results (177 votes), past polls