Greetings Monks,

I'm a high-beginner to intermediate at perl and DBI but this simple issue is eating my lunch.

I have a table of directory information that includes file sizes. I have been adding to the table, reading (select) from the table, etc. for months with no problems. Now I want to add up some selected file sizes. I keep hitting brick walls so I just ask about adding all the file sizes.

From the MySQL command prompt this works:
SELECT SUM(file_size) FROM dir_info;

But, using the same SQL statement inside perl returns a NULL.

With respect to my DB access I am patterning my code from the "MySQL and Perl for the Web" book by Paul DuBois (good book). At a high level I have:
* A DBI connect statement
* The SQL statement shown above stored in $SQLstr
* $sth = $dbh ->prepare($SQLstr);
* $sth -> execute();
* A while(@val = $sth->fetchrow_array()) loop

Many different SELECT statements work OK in my $SQLstr. Adding multiple "where this = that" statements connected by "AND" works OK. I can even use COUNT(*) with no problem. It seems odd to use fetchrow_array for a COUNT but I did not find another function and it worked so I was happy. But, no matter what I do I can't get SUM to work.

By bending the code around to get different error messages and Googling I have gotten hints of column vs. row operations and groupings. These ideas might be on the path to "truth" but it still seems that if the command line works then I should be able to do it in perl.

I have also gotten hints that I need to select in the SQL statement and then use SUM inside the while loop. This seems odd since a "SUM" inside the while loop would not be a SUM in a SQL statement.

Any suggestions or Wisdom?

Thanks,
Bruce

In reply to DBI SUM function by Bruce32903

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