mysql.rar_MYSQL

--注释 --新建一个student表，字段有： --学生编号（主键【唯一表示一条记录】，建议跟业务无关） --学生姓名，年龄，性别，email，地址 --增加一个新列 alter table tb_student add(createdate date) --修改一个列 alter table tb_student modify (sex varchar2(2)) --删除一个列 alter table tb_student drop (createdate) --更改列名 alter table tb_student rename column name to s_name --更改表名 rename tb_student to t_student --注释表 Comment on table tb_student is '学生表'; --注释列 comment on column tb_student.name is '学生姓名'; comment on column tb_student.age is '学生年龄'; comment on column tb_student.sex is '学生性别'; --查看表注释不为空的表 select * from user_tab_comments where comments is not null; --查看列注释不为空的列 select * from user_col_comments where comments is not null; --查看所有列的注释（包括注释为空的列） select * from user_col_comments; --删除表(彻底删除） drop table tb_student --复原被删除的表 flashback table tb_student to before drop; --无法复原的删除 drop table tb_student purge; --删除数据，且无法复原，但保留数据结构 truncate table tb_student --删除数据，可以复原 delete table tb_student select * from tb_student select * from user_tables; select * from user_objects; --查看用户所拥有的表，试图， select * from user_catalog; create table tb_student( id number primary key, name varchar2(18) not null, age number check(age > 18 and age < 40), sex varchar2(2) check(sex='男' or sex='女'), email varchar2(50) unique, address varchar2(50), classNo number, constraints tb_student_fk foreign key(classNo) references tb_class(id) ) create table tb_class( Id number primary key, classNo varchar2(8) not null )