Tim Bunce wrote:
----- Forwarded message from Bob Hunter <[EMAIL PROTECTED]> -----
Date: Tue, 27 Feb 2007 08:03:19 -0800 (PST)
From: Bob Hunter <[EMAIL PROTECTED]>
Subject: DBI's method for reading [row x,field y]
To: Tim Bunce <[EMAIL PROTECTED]>
X-Pobox-Pass: [EMAIL PROTECTED] is whitelisted
Tim,
I am porting an application from Pg to DBI, and make
extensive use of the following method:
Returns the value of the given record and field
number:
$sth->getvalue($rn,$fn)
In particular, I use expressions like
$sth->getvalue($rn+$i,$fn-$j)
where the the number of record/field are displaced by
variables. As far as I can see from your book, DBI has
a method to work one row at the time, in sequence.
This is way too simple to handle the case above. I
looked for a more powerful DBI method, but it does not
seem to exist. Is it so? Please give me an insider's
view of this problem. Does DBI have an equivalent to
Pg' method "getvalue"? If not, can you please copy it
from Pg's module, and make it available in DBI?
Regards,
Bob
So if I understand you correctly, getvalue() takes a row number and a
column number and returns the value of the column with index $fn from
the row with index $rn?
If you are not doing selects with huge result-sets then you can use the
selectall_arrayref method (or fetchall_arrayref) which returns all the
columns for all the rows in the select into an array reference e.g.
$af = selectall_arrayref('select * from table');
print $af->[0]->[0]; # prints first column from first row
print $af->[1]->[1]; # prints second column from second row
(assuming the default in Perl of array indexes starting at 0)
Of course, selectall/fetchall_arrayref retrieves all the rows in the
result-set so this will use that amount of memory up but given you are
already doing this I guess that won't bother you (unless Pg uses cursors
to navigate to the required row). To my knowledge, DBI does not support
fetching only a specific row via a cursor but I'm sure someone will
correct me if I'm wrong on that.
Martin
--
Martin J. Evans
Easysoft Limited, UK
http://www.easysoft.com
