sql基本语句

create table stu (id int, name char, score float);
create table if not exists stu (id int, name char, score float);

drop table stu;

insert into stu values (1, 'bob', 99);
insert into stu (id, name) values (9, 'scott');

select * from stu;

select * from where id<3 and score>90;

select id, name from stu where score > 90;

update stu set score=60 where id=1;

delete from stu where id = 1;
delete from stu; --删除所有

create table stu (id int primary key, name char, score float);

create table b as select * from a;

create table stu1 as select id, name, score from stu;

alter table stu add aolumn score int;

alter table stu rename to stuinfo;

-- 不支持直接修改字段名
-- 1. 重命名
alter table stuinfo rename to stu;
-- 2. 新建修改名字后的表(新建一个 a)
create table stuinfo (name char, age1 int, sex char, score int);
-- 3. 从旧表 b 中取出数据，插入到新表 a 中
insert into stuinfo select * from stu;

-- 不支持直接删除列
-- 1. 创建一个表 b，复制旧表 a 需要保留的字段信息
create table stu as select name, age1, sex from stuinfo;
-- 2. 删除旧表a
drop table stuinfo;
-- 3. 修改新表 b 的名字 a
alter table stu rename to stuinfo;