> i am having a small problem with rows in the DBD::mysql module.
All of the classes and methods you're using come from the 'use DBI'
statement. It is that module with which you are having difficulty, not
DBD::mysql
> more specifically, what I am trying to do is to insert a value in a mysql
> table ONLY if it does NOT exist in there already.
Independent of the Perl-answer to this question, I'd start to wonder if
your algorithm and database structure are sound. Are you sure you
can't restructure so that you don't attempt to add a duplicate value in
the first place? Are you sure you can't restructure so that the value
is a UNIQUE column, and therefore the database prevents the insertion?
> Now I know the queries are
> working ok but its the num rows thats not evaluating properly and thus I am
> getting duplicates in the table that I do not want.
>
> I have read the DBD::mysql doc at CPAN but that didn't solve my problem
DBD::mysql contains only information specific to the database type
you're using. Your problem is with the Perl DBI in general. You
should look at DBI's docs as well.
> Here is a piece of code that I have and that the problem is manifesting
> itself in:
> ======================================
> my $qb = $dbh->prepare("SELECT * FROM stockIndex WHERE pSymbol='$sym'");
> $qb->execute;
> if($qb->rows()==0) {
> if(!$dbh->do("INSERT INTO stockIndex(pSymbol) VALUES('$sym')"))
> {
> print $dbh->errstr;
> }
> }
> $qb->finish();
> =======================================
>
> Can anyone please point out the error in here or give me any idea of what is
> going wrong?
You are making a false assumption about the rows() method. Please read
up on what it actually does:
http://search.cpan.org/~timb/DBI-1.48/DBI.pm#rows
You should also take a look at the Database-specific method of
determining the number of rows in a statement. Search the relevant
MySQL documentation for the "COUNT" function.
Hope this helps,
Paul Lalli
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