SQL settings self-increment, and default

MySQL database increases the self-increment property for the primary key field already in the table :

      ALTER TABLE ' category ' MODIFY COLUMN ' id '  int (one) not NULL auto_increment First, ADD PRIMARY KEY (' id ');

MySQL Database build table settings default add self-increment property:

CREATE TABLE student (SID int PRIMARY KEY auto_increment, stu_id INT UNIQUE,
              Name varchar () not NULL, 中文版 varchar (DEFAULT ' zero '),
              Math float default 0, computer float default 0);

SQL settings self-increment, and default