请教关于打印NULL值的问题

天下第一菜

数据库里有张表
mysql> select * from t9;            
+-----+------+
| n   | m    |
+-----+------+
|  12 | NULL |
|  22 | NULL |
|  32 | NULL |
|  42 | NULL |
|  52 | NULL |
|  62 | NULL |
|  72 | NULL |
| 102 | NULL |
| 112 | NULL |
| 122 | NULL |
+-----+------+


#!/usr/bin/perl
use strict;
use warnings;
use DBI;
my $db_handle=DBI->connect ("DBI:mysql:test:10.0.4.1:3306","aa","bb");
my $t9 = $db_handle->prepare("select * from t9");
$t9->execute();
while (my $row = $t9->fetchrow_hashref())
{
        print $row->{m};
}
$t9->finish();

打印n时候没有问题，但打印m的时候报错
Use of uninitialized value in print at ./a.pl line 10.
Use of uninitialized value in print at ./a.pl line 10.
Use of uninitialized value in print at ./a.pl line 10.
Use of uninitialized value in print at ./a.pl line 10.
Use of uninitialized value in print at ./a.pl line 10.
Use of uninitialized value in print at ./a.pl line 10.
Use of uninitialized value in print at ./a.pl line 10.
Use of uninitialized value in print at ./a.pl line 10.
Use of uninitialized value in print at ./a.pl line 10.
Use of uninitialized value in print at ./a.pl line 10.

请问大家有什么方法可以把NULL当成字符串打印出来？

兰花仙子

请问大家有什么方法可以把NULL当成字符串打印出来？

1. unless (defined($row->{m}) ) {
   
2.     print "Null\n";
   
3. }

复制代码

天下第一菜

谢谢美女哈~