NULL and NOT NULL help please

[VenusJ]

hello,
I am learning how to create a database driven site for one of my classes, and i am a total newbie.

I am creating a database with mysql, however I don't understand how to use NULL and NOT NULL and would like somebody to explain to me and give me example.

I have something like that

CREATE TABLE classroom (
id int(11) NOT NULL auto_increment,
name varchar(250) default NULL,
city varchar(50) default NULL,
states varchar(20) default NULL,
zip varchar(20) default NULL,
PRIMARY KEY (id)
)

my question is when to use NULL and when to use NOT NULL. why are they important? i will create more fields such as datejoin, hobby, and so on, how do i know if i should assign NULL or NOT to the fields?

thank you

[kevinsequeira]

when you specify a column as NOT NULL it means that it has to have a value in it.
If you try to do an insert query into the table but have no value for that column you will get an error.
So you could use it for columns where the data to be entered is complusory for your application.

when you use DEFAULT NULL, it means that if no value is entered it takes NULL as the default value.

you may want to take a look at this link

http://www.mysql.com/doc/en/CREATE_TABLE.html

reg
kevin

[VenusJ]

hello,
thanks, that answer my question, i will read the link now.

thank you 🙂