documentation bugs on LongRealLen

From: Bart Lateur (bart.lateur_at_pandora.be)
Date: 12/10/04

  • Next message: Michael Peppler: "Re: documentation bugs on LongRealLen" 
    To: dbi-users@perl.org
Date: Fri, 10 Dec 2004 01:48:26 +0100

    There's a few bugs in the code of the section of LongReadLen, even in
    the latest version of DBI that is on CPAN. I quote:

            If you can't be sure what value to use you could execute an
            extra select statement to determine the longest value. For
            example:

              $dbh->{LongReadLen} = $dbh->selectrow_array{qq{
                  SELECT MAX(long_column_name) FROM table WHERE ...
              });
              $sth = $dbh->prepare(qq{
                  SELECT long_column_name, ... FROM table WHERE ...
              });

    Bug 1is a typo:

    - $dbh->{LongReadLen} = $dbh->selectrow_array{qq{
    + $dbh->{LongReadLen} = $dbh->selectrow_array(qq{

    Bug 2 is thinko. If your rows contain the values "alpha", "beta", "zeta"
    "omega" in that column, $dbh->{LongReadLen} will be set to "zeta". I
    don't think that will buy us anything good. You want the *length* of the
    *longest* string, not the string that sorts last in the word list. So,
    somebody forgot about length(), or whatever the proper keyword is in
    SQL.

    Unfortunately that keyword is highly unportable. A Google search showed
    me that octet_length() is probably what I'm after, for SQL-92. I tried
    it on MS-Access using DBD::ODBC, and it failed completely. I replaced it
    with the VB keyword "Len", and it worked... more or less.

    One word of caution, with regards to MS-Access. It turned out that
    Len(), when used in Ms-Access' SQL, is actually treated as a string, so
    MAX() returned the wrong result. The max value I got was about 82000,
    while the actual longest string was closer to 180000 bytes. What caused
    it is simply that "8" gt "1".

    Using a numerical context for that function, by adding 0 for example,
    might have helped. I haven't tried it. It was a one shot program anyway. 

    -- 
	Bart.
  • Next message: Michael Peppler: "Re: documentation bugs on LongRealLen"

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