用于SQL查询的Perl串联

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.