Perl concatenation for SQL query - sql

Question

I'm trying to transfer the content of a CSV file into a table in PostgreSQL using Perl.
I'm able to update my table successfully, but the terminal returns an error:
Use of uninitialized value in concatenation (.) or string
Syntax error near ","
INSERT INTO test VALUES (, '', '', '', '',, )
Here is the code where it fails :
for (my $i=0 ; $i<=50; $i++){
$dbh ->do("INSERT INTO test VALUES ('$LastName[$i]', '$Street[$i]', $Balance_account[$i])") ;
If more information is needed just ask them.
Sorry for the bad English.
--
Thomas

Answer 1

Use placeholders,
for (my $i=0 ; $i<=50; $i++){
$dbh->do("INSERT INTO test VALUES (?,?,?)",
undef,
$LastName[$i], $Street[$i], $Balance_account[$i]
);
}
Ideally, you should prepare the query and execute for each set of values, something like this:
my $sth = $dbh->prepare('INSERT INTO test VALUES (?,?,?)');
for (my $i=0 ; $i<=50; $i++){
$sth->execute($LastName[$i], $Street[$i], $Balance_account[$i]);
}

Answer 2

My guess is that your error is being caused by not specifying the column names in your insert, while simultaneously having the wrong number/types of columns. I would expect the following Perl code to not error out:
for (my $i=0 ; $i<=50; $i++){
$dbh -> do("INSERT INTO test (lastname, street, balance) VALUES ('$LastName[$i]', '$Street[$i]', $Balance_account[$i])");
Here is what a working query might look like:
INSERT INTO test (lastname, street, balance)
VALUES
('Skeet', '100 Thatcher Street', 100.50);
It is generally considered bad practice to not include column names while doing an insert, because even if you get it right, it could easily break later on.