【MySqL】基本命令之数据约束

create table 默认约束(
    -> name VARCHAR(10),
    -> age INT UNSIGNED DEFAULT 18
-> );

create table 非空约束(
    -> name VARCHAR(20), ###插入字符长20的name
    -> sale INT NOT NULL, ###插入非空的字符串
    -> year INT NOT NULL DEFAULT 2022 ###插入非空的字符串，默认值为2022
    -> );

create table 唯一约束_lie(
    -> id INT UNSIGNED UNIQUE,
    -> name VARCHAR(10) UNIQUE
    -> );

create table 唯一约束_biao(
    -> id INT UNSIGNED,
    -> name VARCHAR(10),
    -> UNIQUE(id),
    -> UNIQUE(name)
    -> );

create table 主键约束(
    -> id INT UNSIGNED PRIMARY KEY,
    -> name VARCHAR(20)
    -> );

ALTER TABLE 主键约束 DROP PRIMARY KEY

ALTER TABLE my_primary MODIFY id INT UNSIGNED;

create table 自动增长(
    -> id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
    -> name VARCHAR(20)
    -> );