Isn't PHP's null value equal to MySQL's null value? [duplicate]

Answer 1

That is because PHP null is converted into the empty string "" when you create the query string.

$variable = null;
$insert = "insert into mytable set mycolumn = $variable" ;
echo $insert;

Will produce:

insert into mytable set mycolumn = 

To fix your query you would need to check if the PHP variable is null and change it to string NULL. (Also now mentioned in the comment of @MarkB.)

if ($variable == null){
    $variable = "NULL";
}

This will produce:

"insert into mytable set mycolumn = NULL"

Note that NULL has no " around it because it is now concatenated to the other string.

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*(note: insert into tablename set .. is not correct, you either insert data or you update tablename set data.)