MySQL, how to insert null dates

Question

I am having trouble inserting null values into date fields into a MySQL table.

Here is the insert query:

$query = 'INSERT INTO table (column_s1, column_s2, column_d1, column_d2)
VALUES ("'.$string1.'", "'.$string2.'", '.$date1.', '.$date2.')';

Columns s1 and s2 take string values and d1 and d2 take dates. When I run this query with only the string fields, there is no problem.

The date values can be either set or null, so I have not included the quotation marks in the query, but have instead added them to the variable earlier on. This is the php code I am using to set the date values:

if (empty($date1)){
    $date1 = NULL;
}
else{
    $date1part = explode("/",$date1);
    $date1 = '"'.$date1part[2].'/'.$date1part[1].'/'.$date1part[0].'"';
}

When the date values are all set, the record is inserted correctly. However, when either of the dates is null, nothing is inserted.

Why can't I just insert null values into MySQL like this?

Answer 1

In Mysql DATE data type Default NULL means

Some version set as 0000-00-00

Some version set as 1970-01-01