1.唯一约束
创建班级表 tb_class
CREATE TABLE tb_class( id INT PRIMARY KEY AUTO_INCREMENT, name VARCHAR(10) UNIQUE );
2.查看建表时的细节
语法:SHOW CREATE TABLE tb_name;
SHOW CREATE TABLE tb_class;
3.外键约束
创建学生表 tb_student(子表),外键引用tb_class(主表)的id,表示该学生属于哪个班级
CREATE TABLE tb_student( id INT PRIMARY KEY AUTO_INCREMENT, name VARCHAR(20), pid INT, FOREIGN KEY(pid) REFERENCES tb_class(id) );
4.添加单列
语法:ALTER TABLE tb_name ADD [COLUMN] col_name column_definition [FIRST | AFTER col_name]
ALTER TABLE tb_student ADD COLUMN age INT;
5.删除单列
语法:ALTER TABLE tb_name DROP [COLUMN] col_name
ALTER TABLE tb_student DROP age;
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