MySQL将NULL值插入INT列

Question

I know that this question has been asked before. I found the post, however, it did not solve my problem as my column does allow null.

I want to insert a NULL value into my integer column.

if ($startYear == "") {
    $startYear = NULL;
}

mysqli_query($con, "INSERT INTO Application (startYear) VALUES ('".$startYear."')");

Before you ask, I have checked if $startYear is ever empty, and it is, so this should work.

When I run this query it inputs a 0 into the database row. It does not insert NULL like I want.

Here is my column's structure:

http://i.imgur.com/XuWq9Km.png

One important thing is that, I can not modify the column's structure. It is off limits.

Thanks in advance.

Answer 1

The issue is you're not actually inserting into the query the string 'NULL', but a php null , which makes your query insert empty string, this gets coverted to 0 in the DB.

You'd need to do this:

  mysqli_query($con, "INSERT INTO Application (startYear) VALUES (NULL)");

Answer 2

you're inserting a PHP null value, which when used in a string context becomes an empty string - which is what was originally. You have to insert a literal string with the letters n , u, l , l` for this to work:

if ($startYear == '') {
   $startYear = 'NULL'; // string null
}
$sql = "INSERT ..... VALUES ($startYear)";

which would produce

INSERT ... VALUES (NULL)

To expand:

   $foo = null; // actual PHP null value
   $bar = "$foo"; // insert this php null into a string
   echo strlen($bar); // returns 0

   $foo = 'null' // string with 4 letters: n,u,l,l
   $bar = "$foo";
   echo strlen($bar); // returns 4