How does php write a NULL value to the mysql field? _ PHP Tutorial

How does php write a NULL value to the mysql field ?. Problem: When modifying the house information, there is a field that is the total number of floors floorall, which is the int field. if you enter the value of this field when modifying the information, write the value to the database. Problem:

When modifying the house information, one field is the total floor count floorall, which is the int field and can be empty.
When modifying information, if the value of this field is entered, the value is written to the database. If no value is entered, NULL is written to the database.
How to implement it?

I wrote it like this.
If ($ floorall = '') {$ floorall = NULL ;}
$ Db-> query ("updata tabel set floorall = '$ floorall '");
The written value is 0 instead of NULL.

Answer:

Hello, please execute the following statement:

Updata tabel set floorall = null

When you modify the house information in the upper-right corner, there is a floorall field in the total floor number, which is an int field. if you enter this field when modifying the information, write the value to the database...