Beefy Boxes and Bandwidth Generously Provided by pair Networks
Perl: the Markov chain saw
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??
I have a Postgres table with more than 8 million rows. Given the following two ways of doing the same query, I get wildly different results.

$q .= '%'; ## query 1 my $sql = qq{ SELECT a, b, c FROM t WHERE Lower( a ) LIKE '$q' }; my $sth1 = $dbh->prepare($sql); $sth1->execute(); ## query 2 my $sth2 = $dbh->prepare(qq{ SELECT a, b, c FROM t WHERE Lower( a ) LIKE ? }); $sth2->execute($q);

query 2 is at least an order of magnitude slower than query 1... seems like it is not using the indexes, while query 1 is using the index.

Would love hear why.



when small people start casting long shadows, it is time to go to bed

In reply to same query, different execution, different performance by punkish

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 rifling through the Monastery: (5)
    As of 2014-07-29 06:55 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      My favorite superfluous repetitious redundant duplicative phrase is:









      Results (211 votes), past polls