RE: NULL values returning as empty string

From: Larry Low <llow(at)telesphere.com>
Date: Tue Oct 23 2007 - 13:34:26 EDT

Actually this was a bug in 5.0.22 client showing empty strings as NULL.

---

Larry Low
4150 N Drinkwater Blvd., 5th Floor
Scottsdale, AZ 85251
Office: 480.385.7045
E-mail: llow@telesphere.com'

Telesphere Networks, Inc

-----Original Message-----
From: Larry Low [mailto:llow@telesphere.com] Sent: Tuesday, October 23, 2007 10:02 AM To: perl@lists.mysql.com
Subject: RE: NULL values returning as empty string

Nevermind it seems the thold_hi field is a VARCHAR and the program filling it is putting in the string NULL.

---

Larry Low
4150 N Drinkwater Blvd., 5th Floor
Scottsdale, AZ 85251
Office: 480.385.7045
E-mail: llow@telesphere.com'

Telesphere Networks, Inc

-----Original Message-----
From: Larry Low [mailto:llow@telesphere.com] Sent: Tuesday, October 23, 2007 9:59 AM
To: perl@lists.mysql.com
Subject: NULL values returning as empty string

I am unable to figure out why but NULL values which from what I read should be undefined are being defined. See the example below for the column thold_hi which shows as NULL in the database but the reference $row->{'thold_hi'} being defined.

I am running mysql 5.0.22 and DBI 1.58.

Example:

my $sql = "SELECT t.lastread,t.thold_hi,t.thold_low,thold_alert,bl_alert FROM host h LEFT JOIN data_local dl ON h.id=dl.host_id LEFT JOIN data_template_rrd dr ON dr.local_data_id=dl.id LEFT JOIN thold_data t ON t.data_id=dr.id WHERE h.description='something' AND dr.data_source_name='hdd_free'";

my $sth = $dbh->prepare($sql);
$sth->execute();
my $row = $sth->fetchrow_hasref();

if (!defined($row->{'thold_hi'})) {

        print "Not Defined\n";
} else {

        print "Defined\n";
}

mysql> SELECT t.lastread,t.thold_hi,t.thold_low,thold_alert,bl_alert FROM host
h LEFT JOIN data_local dl ON h.id=dl.host_id LEFT JOIN data_template_rrd dr ON
dr.local_data_id=dl.id LEFT JOIN thold_data t ON t.data_id=dr.id WHERE h.description='something' AND dr.data_source_name='hdd_free'; +----------+----------+-----------+-------------+----------+ | lastread | thold_hi | thold_low | thold_alert | bl_alert | +----------+----------+-----------+-------------+----------+ | 24997856 | NULL | 25000000 | 1 | 0 | +----------+----------+-----------+-------------+----------+ 1 row in set (0.00 sec)

---

Larry Low
4150 N Drinkwater Blvd., 5th Floor
Scottsdale, AZ 85251
E-mail: llow@telesphere.com'

Telesphere Networks, Inc

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For list archives: http://lists.mysql.com/perl To unsubscribe: http://lists.mysql.com/perl?unsub=lists@pantek.com Received on Tue Oct 23 13:34:35 2007