drop database xxx

    —删除数据（避免这么写，删除表全部数据）
    DELETE FROM student

    —删除指定数据
    DELETE FROM student WHERE id = 1;

    <—删除连贯数据,可以用between and—>
    delete from t_emp where id Between 23 and 99;

    <—删除散列数据，可以用in—>
    delete from t_emp where id in(3,5,6,8);


    —TRUNCATE的作用：完全清空一条数据库表，表的结构和索引约束不会变！
    —清空 student 表
    TRUNCATE student