In PHP, what is the differences between NULL and setting a string to equal 2 single quotes

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Null is just another datatype in PHP, which has only one value (null). Since PHP is a loosly typed language, it can be confusing how it handles different values.

"", 0, "0", False, array(), Null are all considered False in PHP.

Null, however, is a different kind of animal. The main incompatibility with using Null is that you cannot tell if it isset().

$x = false;
isset($x)  ->  true
echo $x    ->  ""

$y = null;
isset($y)  ->  false
echo $y    ->  ""

//$z is not set
isset($z)  ->  false
echo $z    ->  E_NOTICE

So null is odd in the sense that it doesn’t follow normal variable rules in PHP (at least some). In most cases, it is fine.

When it comes to database columns, PHP’s NULL has no place there. You see, SQL is a string based language. SQL’s NULL must be represented by NULL with no quotes.

So if you want an EMPTY field, set it to “”

INSERT INTO foo SET bar = ""

But if you want a NULL field, set it to NULL

INSERT INTO foo SET bar = NULL

BIG DIFFERENCE.

But if you try to insert the PHP NULL directly, it will add zero characters to the query, (which leaves you with a blank or syntax error, depending on if you quoted it).

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