Insert NULL into a PostgreSQL DB via PHP when a date field is empty

Question

I have a csv data set containing a date field which my may or may not be empty (=''). I've set Postgres to allow null on this field, and have given it the Date format. When I run my PHP import script (below), the import fails because the empty string is not in the date format. My understanding is that I should set it to NULL, which I want to do only if the field is in fact empty. So I want to conditionally set it, which I thought would work like:

    <?php if (empty($data[3])){
          $data[3] = NULL;
         // (i've tried "null", 'null', "NULL", null, etc.)

When I execute the import via this method, whenever the date field is empty, I get PHP Warning: pg_query(): Query failed: ERROR: invalid input syntax for type date: "NULL". Can PHP not pass NULL into a pg_query? Should I be putting the conditional logic inside the query instead? My code is below. Thank you very much for any advice.

<?php
$conn_string = "host=localhost port=5432 dbname=mydb user=myusername password=mypassword";
$_db = pg_connect($conn_string);

$fileName = "../feeds/stale_prod_report.20111215.csv";
$row = 0;

if ($_db->connect_error) {
die('Connection Error (' . $_db->connect_errno . ') ' . $_db->connect_error);
}

if (($handle = fopen($fileName, "r")) !== FALSE) {
while (($data = fgetcsv($handle, 1000, ",")) !== FALSE) {
    $num = count($data);
    $row++;
    for ($c=0; $c < $num; $c++) {
        $data[$c] = pg_escape_string(utf8_encode($data[$c]));
    } 

    //if date is empty, insert a dummy - not accepting null
    if (empty($data[16])){
        $data[16] = NULL;
    }

    if($row !== 1){
        pg_query($_db, "INSERT INTO product (first_field, second_field, 
        third_field, my_date) 
    VALUES ('$data[0]', '$data[1]', '$data[2]', '$data[3]')";
}
fclose($handle);

} else {echo "Could not find the file!";}

Answer 1

Your problem is that you have single quotes inside your SQL:

INSERT INTO product (first_field, second_field, third_field, my_date) 
VALUES ('$data[0]', '$data[1]', '$data[2]', '$data[3]')

so if $data[0] is the string "NULL", you'll end up with this:

INSERT INTO product (first_field, second_field, third_field, my_date) 
VALUES ('NULL', ...

and you'll be trying to insert a string that contains NULL rather than the NULL literal itself. You'll have to do your quoting inside the $data values rather than inside your SQL:

# Warning: my PHP is a bit rusty but I think this is right
if(empty($data[0])) {
    $data[0] = "NULL";
}
else {
    $data[0] = "'" . pg_escape_string(utf8_encode($data[$c])) . "'";
}

And then later:

pg_query($_db, "INSERT INTO product (first_field, second_field, third_field, my_date) 
    VALUES ($data[0], $data[1], $data[2], $data[3])";

Or better, switch to PDO and use prepared statements.