Fetching one single row from database using Perl - perl

Question

I am trying to run a simple database connection with Perl using postgreSQL
use DBI;
$database = "postgres";
$user = "postgres";
$password = "admin";
my $dbh = DBI->connect( "dbi:Pg:dbname=$database"
, $user
, $password
)
or die "Can't Connect to database: $DBI::errstr\n";
# get data from the URL string
my $firstname = "haroon";
my $lastname ="ash";
my $age = 24;
# insert the data into the database
my $query = "INSERT INTO people (firstname, lastname, age)
VALUES ('$firstname','$lastname', '$age')";
$dbh->do($query);
# get the ID of the inserted person
$query = "SELECT MAX(id) FROM people";
my $sth = $dbh->prepare($query);
my $rv =$sth->execute;
if($rv < 0){
print $DBI::errstr;
}
else {
my $row = $sth->fetchrow_hashref;
my $person_id = $row->{'max'};
print $firstname, $lastname
. "was successfully inserted at position "
. $person_id;
}
I am trying to print the person id which i had entered latest. But my $person_id = $row->{'max'} seems to give me the correct answer instead of my $person_id = $row->{'id'};. I am not understanding why is that.

Answer 1

You might want to set column alias for query,
$query = "SELECT MAX(id) AS id FROM people";
as postgres is putting his own alias for you, and that is max.
If all you want is last inserted id, you can
my $query = "INSERT INTO people (firstname, lastname, age)
VALUES (?,?,?)
returning id
";
and fetch query as you would do with select. (check pg docs)

Answer 2

You can use the RETURNING keyword to return the id associated with the row you just inserted:
my $query = '
INSERT INTO people (firstname, lastname, age)
VALUES ($1, $2, $3)
RETURNING id';
my $sth = $dbh->prepare($query);
$sth->execute($firstname, $lastname, $age);
my $rv = $sth->fetchrow_hashref();
printf "%s, %s was successfully inserted at position %d\n",
$firstname, $lastname, $rv->{id};

Answer 3

You did not enter a PERSON_ID in your insert statement.
Instead it seems the ID field was populated by the DB, an auto increment value during insert, it seems.
Without knowing the table definition (and potential insert trigger on the table) it is hard/impossible to give you a better answer.