Not NULL and null_php tips

Not NULL | Null: Specifies whether the column is allowed to be empty. If NULL is not specified and NOT NULL is specified, the column is considered to specify NULL
In MySQL,
Sets a null value for a not NULL field.
It's not going to go wrong,
MySQL automatically converts the null value to the default value of the field.
I'm afraid you didn't explicitly set the default value for the field when the table was defined
: "In general, MySQL will automatically add the default value for you,

Like what
Assigns a null value to an integral of not NULL.
The result is 0.

CHAR type
-> ' null value

Datatime
-> ' 0000-00-00 00:00:00 '

Wait a minute
Top

2 floor unicorn_bx (every day sky blue) reply to 2003-01-13 11:22:18 score 0 that is, not NULL in MySQL is not a constraint.

If the field is set to NULL, the value of the field is not given when the record is inserted, then MySQL automatically uses the value of default, and if there is no default, the field value is null regardless of what type the field is.

This is not the effect of NOT null and NULL in MySQL, that is, when the default value is not defined, the defaults are given differently.