非空约束和默认值约束

-- 非空约束：not null
CREATE TABLE student(
    id int PRIMARY KEY AUTO_INCREMENT,
  name varchar(20) UNIQUE NOT NULL
);
INSERT INTO student (name) VALUES(NULL);

-- 默认值约束 default
CREATE TABLE student(
    id int PRIMARY KEY AUTO_INCREMENT,
  name varchar(20) UNIQUE NOT NULL,
  gender varchar(6) DEFAULT 'male'    -- 不传值时给定默认值为male
);

INSERT INTO student (name,gender) VALUES ('mayun','male');
INSERT INTO student (name,gender) VALUES ('mahuateng1',NULL);#不会把null变成默认
INSERT INTO student (name) VALUES ('mahuateng');