Reaped: Perl DBI NULL and undef

NodeReaper has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Perl DBI NULL and undef by Marshall (Canon) on Aug 22, 2012 at 02:38 UTC
my $sth = $dbh->prepare("select NAME from data_template_data"); my $results = $sth->execute() or die "execute failed"; # the return value from $sth->execute() will be undef # if the query failed...otherwise the $results value # will contain the number of lines in that result set # # The DBI will return "0E0" to mean a true value with # a numeric result of "zero" to differentiate between # "didn't work" (undef) and "worked, but returned no rows" # this is the "logically true, but numeric false value". #To get the rows, use a while() loop.. # while ( (my $name) = $sth->fetchrow()) { print "name is $name\n"; } [download] I don't know the schema for your DB. But in general, you will get a NULL for for a blank field instead of undef, but there are exceptions. There are "rules" for the fields that are specified when the table is created. If you can give me some data, I can create a MySQL DB on my server and help you further. Don't go "crazy", just give me 5-10 lines or so.	[reply] [d/l]
Re^2: Perl DBI NULL and undef by chefchanyu (Novice) on Aug 22, 2012 at 03:43 UTC
INSERT INTO data_template_data (id, local_data_template_data_id, local +_data_id, data_template_id, data_input_id, t_name, name, name_cache, +data_source_path, t_active, active, t_rrd_step, rrd_step, t_rra_id) V +ALUES (3, 0, 0, 3, 2, 'on', '\|host_description\| - Hard Drive Space', '', N +ULL, '', 'on', '', 300, ''), (4, 0, 0, 4, 1, '', '\|host_description\| - CPU Usage - System', '', N +ULL, '', 'on', '', 300, ''), (5, 0, 0, 5, 1, '', '\|host_description\| - CPU Usage - User', '', NUL +L, '', 'on', '', 300, ''), (6, 0, 0, 6, 1, '', '\|host_description\| - CPU Usage - Nice', '', NUL +L, '', 'on', '', 300, ''), (7, 0, 0, 7, 2, 'on', '\|host_description\| - Noise Level', '', NULL, +'', 'on', '', 300, ''), (8, 0, 0, 8, 2, 'on', '\|host_description\| - Signal Level', '', NULL, + '', 'on', '', 300, ''), (9, 0, 0, 9, 2, 'on', '\|host_description\| - Wireless Transmits', '', + NULL, '', 'on', '', 300, ''), (10, 0, 0, 10, 2, 'on', '\|host_description\| - Wireless Re-Transmits' +, '', NULL, '', 'on', '', 300, ''), (11, 0, 0, 11, 4, '', '\|host_description\| - Load Average', '', NULL, + '', 'on', '', 300, ''), (13, 0, 0, 13, 6, '', '\|host_description\| - Memory - Free', '', NULL +, '', 'on', '', 300, ''), (15, 0, 0, 15, 6, '', '\|host_description\| - Memory - Free Swap', '', + NULL, '', 'on', '', 300, ''), (16, 0, 0, 16, 7, '', '\|host_description\| - Processes', '', NULL, '' +, 'on', '', 300, ''), (17, 0, 0, 17, 5, '', '\|host_description\| - Logged in Users', '', NU +LL, '', 'on', '', 300, ''), (18, 0, 0, 18, 10, '', '\|host_description\| - Ping Host', '', NULL, ' +', 'on', '', 300, ''), (19, 0, 0, 19, 1, '', '\|host_description\| - Total Users', '', NULL, +'', 'on', '', 300, ''), (20, 0, 0, 20, 1, '', '\|host_description\| - Total Logins', '', NULL, + '', 'on', '', 300, ''), (22, 0, 0, 22, 1, '', '\|host_description\| - File System Reads', '', +NULL, '', 'on', '', 300, ''), (23, 0, 0, 23, 1, '', '\|host_description\| - File System Writes', '', + NULL, '', 'on', '', 300, ''), (24, 0, 0, 24, 1, '', '\|host_description\| - Cache Checks', '', NULL, + '', 'on', '', 300, ''), (25, 0, 0, 25, 1, '', '\|host_description\| - Cache Hits', '', NULL, ' +', 'on', '', 300, ''), (26, 0, 0, 26, 1, '', '\|host_description\| - Open Files', '', NULL, ' +', 'on', '', 300, ''), (27, 0, 0, 27, 1, '', '\|host_description\| - 5 Minute CPU', '', NULL, + '', 'on', '', 300, ''), (30, 0, 0, 30, 1, '', '\|host_description\| - Load Average - 1 Minute' +, '', NULL, '', 'on', '', 300, ''), (31, 0, 0, 31, 1, '', '\|host_description\| - Load Average - 5 Minute' +, '', NULL, '', 'on', '', 300, ''), (32, 0, 0, 32, 1, '', '\|host_description\| - Load Average - 15 Minute +', '', NULL, '', 'on', '', 300, ''), (33, 0, 0, 33, 1, '', '\|host_description\| - Memory - Buffers', '', N +ULL, '', 'on', '', 300, ''), (34, 0, 0, 34, 1, '', '\|host_description\| - Memory - Free', '', NULL +, '', 'on', '', 300, ''), (35, 0, 0, 35, 2, 'on', '\|host_description\| - Volumes', '', NULL, '' +, 'on', '', 300, ''), (36, 0, 0, 36, 2, 'on', '\|host_description\| - Directory Entries', '' +, NULL, '', 'on', '', 300, ''), (37, 0, 0, 37, 11, 'on', '\|host_description\| - Hard Drive Space', '' +, NULL, '', 'on', '', 300, ''), (38, 0, 0, 38, 2, 'on', '\|host_description\| - Errors/Discards', '', +NULL, '', 'on', '', 300, ''), (39, 0, 0, 39, 2, 'on', '\|host_description\| - Unicast Packets', '', +NULL, '', 'on', '', 300, ''), (40, 0, 0, 40, 2, 'on', '\|host_description\| - Non-Unicast Packets', +'', NULL, '', 'on', '', 300, ''), (41, 0, 0, 41, 2, 'on', '\|host_description\| - Traffic', '', NULL, '' +, 'on', '', 300, ''), (55, 0, 0, 42, 2, '', '\|host_description\| - CPU Utilization', '', NU +LL, '', 'on', '', 300, ''), (56, 0, 0, 43, 12, '', '\|host_description\| - Hard Drive Space', '', +NULL, '', 'on', '', 300, ''), (57, 0, 0, 44, 12, '', '\|host_description\| - CPU Utilization', '', N +ULL, '', 'on', '', 300, ''), (58, 0, 0, 45, 1, '', '\|host_description\| - Processes', '', NULL, '' +, 'on', '', 300, ''), (59, 0, 0, 46, 1, '', '\|host_description\| - Logged in Users', '', NU +LL, '', 'on', '', 300, ''), (62, 13, 3, 13, 6, NULL, '\|host_description\| - Memory - Free', 'Loca +lhost - Memory - Free', '<path_rra>/localhost_mem_buffers_3.rrd', NUL +L, 'on', NULL, 300, NULL), (63, 15, 4, 15, 6, NULL, '\|host_description\| - Memory - Free Swap', +'Localhost - Memory - Free Swap', '<path_rra>/localhost_mem_swap_4.rr +d', NULL, 'on', NULL, 300, NULL), (64, 11, 5, 11, 4, NULL, '\|host_description\| - Load Average', 'Local +host - Load Average', '<path_rra>/localhost_load_1min_5.rrd', NULL, ' +on', NULL, 300, NULL), (65, 17, 6, 17, 5, NULL, '\|host_description\| - Logged in Users', 'Lo +calhost - Logged in Users', '<path_rra>/localhost_users_6.rrd', NULL, + 'on', NULL, 300, NULL), (66, 16, 7, 16, 7, NULL, '\|host_description\| - Processes', 'Localhos +t - Processes', '<path_rra>/localhost_proc_7.rrd', NULL, 'on', NULL, +300, NULL), (68, 0, 0, 47, 1, '', '\|host_description\| - Memory - Cache', '', NUL +L, '', 'on', '', 300, ''), (69, 0, 0, 48, 1, 'on', '\|host_description\| -', '', NULL, '', 'on', +'', 300, ''), (70, 0, 0, 49, 0, '', '10 minutes', '', NULL, '', 'on', '', 600, '') +, (71, 70, 8, 49, 0, NULL, '10 minutes', '10 minutes', '/var/www/cacti +_rrd/MMS/Daily/CDR_TOTAL_901S902M905S906WAPENC.rrd', NULL, 'on', NULL +, 600, NULL), (72, 70, 9, 49, 0, NULL, '10 minutes', '10 minutes', '/var/www/cacti +_rrd/MMS/Daily/CDR_TOTAL_901R902M905S906FOREIGNOPTUS.rrd', NULL, 'on' +, NULL, 600, NULL); [download]	[reply] [d/l]