How do I insert a NULL value - php

Question

I want to insert a NULL value into a table column containing the phone area code with the following properties:
mediumint unsigned DEFAULT NULL
In my PHP script, I have this check to convert an empty string to a NULL value:
if($_POST['area_code'] == "") $_POST['area_code'] = NULL;
// clean POST
foreach($_POST as $field => $value)
{
$string[] = $field."=".$value;
}
$sql = "UPDATE Buyer SET ".implode(", ", $string)." WHERE user='$user'";
However, I am getting 0 instead of NULL value. What should I do to insert a NULL?

Answer 1

Your statement needs to look like
UPDATE ... SET area_code = NULL ...
If you're casting a PHP null to a string as you do, it'll just cast to "", i.e. an empty string. You'll need to change the value to "NULL" (the string "NULL") instead of just NULL (the type null). You should also seriously escape/sanitize/validate your values before you plug them into an SQL query, you're wide open for SQL injection.

Answer 2

From http://php.net/manual/en/language.types.string.php
NULL is always converted to an empty string.
when you build $string[], you can't just concatenate your $value, or your nulls will be converted to empty strings, which convert back to zero. You'll have to do a test like:
$value == '' ? 'NULL' : $value

Answer 3

Change PHP NULL to MySQL NULL(string):
if($_POST['area_code'] == '') $_POST['area_code'] = 'NULL';

Answer 4

NULL is always converted to an empty string.
Try
if($_POST['area_code'] == "") $_POST['area_code'] = "NULL";
because null isn't a string

Answer 5

Try it like this:
if($_POST['area_code'] == "") $_POST['area_code'] = "NULL";

Answer 6

For starters, you should be escaping these posted values (maybe you already are). Secondly, NULL in PHP is always converted to an empty string (http://php.net/manual/en/language.types.string.php). Instead, use:
$_POST['area_code'] = 'NULL';
Which will then correctly create the string:
area_code=NULL
for your UPDATE statement.

Answer 7

If your database table column data type is defined as int/float/numeric then it takes 0 instead of NULL. Because what you are doing is, making it as string that does not matches with column definition which was int/float.

Answer 8

That's because you cast your NULL to string:
$field."=".$value
You have two alternatives:
Code an exception for NULL values:
if( is_null($value) ){
$string[] = $field . '=NULL';
}else{
// Please note I've also added proper string escaping
$string[] = $field . "='" . mysql_real_escape_string($value) . "'";
}
Switch to a library that supports prepared statements (IMHO, the simplest and most reliable solution):
$string[] = $field . '=?';
$params[] = $value;