[SOLVED] 2 noobish mysql question

[asmith]

1.when creating table i've seen a lot , they've used "NOT NULL" , like  (username varchar (65) NOT NULL... or NOT NULL default ,

is that for security  ? what does it mean ? what does default mean ?

 

2. i want to put a "id" column in one table  , when first user information fills in the first row, there will be 1 in "id" column , then when second comes, it automaticlly put 2 in id ,

is there any specific code for that ?

[revraz]

NOT NULL means that field cannot be empty.

 

Auto Increment will increment the ID when a new row is created.

 

These are both MySQL features, not PHP.