SQL> create table mje (a int, b varchar(10) null default null);
SQLRowCount returns -1
SQL> insert into mje (a,b) values(1,'fred');
SQLRowCount returns 1
SQL> insert into mje (a,b) values(2, '');
SQLRowCount returns 1
SQL> insert into mje (a) values(3);
SQLRowCount returns 1
SQL> select * from mje;
+------------+-----------+
| a          | b         |
+------------+-----------+
| 1          | fred      |
| 2          |           |
| 3          |           |
+------------+-----------+
SQLRowCount returns -1
3 rows fetched

[download]
perl -MDBI -le 'my $h = DBI->connect; use Data::Dumper; my $r = $h->se
+lectall_arrayref("select * from mje");print Dumper($r);'
$VAR1 = [
          [
            1,
            'fred'
          ],
          [
            2,
            ''
          ],
          [
            3,
            undef
          ]
        ];

[download]

So empty strings in this case are defined and NULLs in the databases are returned as undef in Perl. undef is a Perl thing and NULL is a SQL thing so when you say "How can I separate the undef data and NULL data" it does not make sense.

In reply to Re: Perl DBI NULL and undef by mje
in thread Perl DBI NULL and undef by chefchanyu

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