How does PHP set the value of the variable $value 1 to NULL?

// $runoob_author= "rookie station";

//$ run OOB _ count = NULL；

$sql="INSERT INTO countnull_tbl "。

“(runoob_author，runoob_count)”。

"values"

// "('$runoob_author '，' $ runoob _ count ')"；

"('rookie station', null)";

* The result of annotated method is 0, and the result without annotation is NULL；;

Personal analysis is for reference only: runoob_count is defined as an integer when creating a data table, and "$runoob_count" in ("$runoob_author" and "$runoob_count") is equivalent to "NULL" and is a string type. When it is inserted into the data table as data, there will be a new data type conversion, that is, the string will be converted into an integer.

& lt？ Server-side programming language (abbreviation of professional hypertext preprocessor)

$ a = null

$ b = " null

$ c =(int)$ a；

$ d =(int)$ b；

echo "a= "。 $ a；

Echo "& ltbr >；; ;

echo "b= "。 $ b；

Echo "& ltbr >；; ;

echo "c= "。 $ c；

Echo "& ltbr >；; ;

echo "d= "。 $ d；