ww的笔记之数据库基本操作

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1.创建表
    （1）create table Students(id varchar(16),name varchar(16),score varchar(6));
       （2）create table if not exists Students(id varchar(16),name varchar(16),score varchar(6));
2.删除表
   drop table Students;
3.插入
   （1）insert into Students values(1,'YueBuQun',75);
      (2)自增形式插入：inser into WuGong(name) values('zixiashengong');

4.查看
   (1)查看单个表
       select * from Students;(*代表查看所有字段，可以查看单个字段)
   (2)查看多个表元素
       select Students.id,Students.name,WuGong.name from Students,WuGong where Students.id=WuGong.id;
   (3)条件查看
       select * from Students where score>75 and score<90
      (4)排序查看
       1)正序
              select * from Students order by score;
          2倒序
           select * from Students order by score desc;
   (4)只看两条
       select * from Students limit 2;
    （5）查看有多少条数据
             select count(*)from Students;
   （6）平均分，总和分
           select sum(score)from Students;
       select div(score)from Students;
5.修改
   update Students set score=90 where id=1;
6.删除
   delete from Students where id=3;
7.设置主键和唯一键
   （1）create table if not exists WuGong(id INTEGER primary key autoincrement,name TEXT unique);
   （2）自增形式插入：inser into WuGong(name) values('zixiashengong');

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