db_query for delete is not working in PHP code, but is executing fine directly in mysql

Question

When I run this script on my site, it does not delete any rows, even though the output shows that the query was successful (It outputs the delete query written out, for now). When I run the query in mysql directly, it does delete the rows.

    if (db_query("DELETE FROM {watchdog} WHERE ((type = 'user' AND message IN ('Session opened for %name.', 'Session closed for %name.', 'New user: %name (%email).')) OR type = 'access denied' OR (type = 'smtp' AND message = 'Sending mail to: @to')) AND hostname = '%s'", array($hostname)))
    {
      echo "<br />DELETE FROM watchdog WHERE ((type = 'user' AND message IN ('Session opened for %name.', 'Session closed for %name.', 'New user: %name (%email).')) OR type = 'access denied' OR (type = 'smtp' AND message = 'Sending mail to: @to')) AND hostname = '$hostname'";
    }
    else
    {
      echo "<br />could not delete $hostname ";
    }

There are no error messages on screen or in any logs.

Answer 1

Turns out I had to escape the percent signs

 ('Session opened for %name.', 'Session closed for %name.', 'New user: %name (%email).')) 

becomes

 ('Session opened for %%name.', 'Session closed for %%name.', 'New user: %%name (%%email).'))