1. 增
- 添加一整条数据
insert into my_test values(0,'小明',0,'1999-1-1',0);
- 添加不完整数据
insert into my_students(name) values('小家电');
- 添加多条数据
insert into my_test(name) values('阿姨'),('神雕'),('郭襄');
2. 删
- 物理删除
delete from stus where id=5;
3. 改
- 修改某条数据
update students set birthday='1990-2-2' where id=2
4. 查
- 查看列表所有数据
select * from my_test;
- 筛选数据
select * from stus where isdelete=0;
- 逻辑与运算与或非
and,or,not
select * from stus where name='小米' and isdelete=0;
- 模糊查询
# %表示任意多个字符
select * from stus where name like '小%';
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# 下划线数量表示占位符数量
select * from stus where name like '小_'；
- 范围查询
select * from stus where id in (1,4,6);
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# 编号3-8的男生
select * from stus where id between 3 and 8 and gender=1;
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- 空判断
# null 与 ‘’ 是不同的
select * from stus where birthday is null;
select * from stus where birthday is not null;
- 优先级
# 小括号>not>比较运算符>逻辑运算符
# and > or
4.1 聚合
- 求总数 count()
select count(*) from stus where isDelete=0;
- 最大值 max()
select max(id) from stus;
- 最大值 min()
select min(id) from stus;
- 平均值 avg()
select avg(id) from stus;
- 求和 sum()
select sum(id) from stus where gender=1;
4.2 分组
- 统计男女生人数
select gender,count(*) from stus group by gender;
- 分组后筛选
select gender,count(*) from stus group by gender having gender=0;
select gender,count(*) from stus group by gender having count(*)>2;
select gender,count(*) as rs from stus group by gender having rs>2;
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4.3 排序 select * from 表 order by 列1 asc|desc,列2 asc|desc,...
- 默认由小到大
# 男生按id降序排列
select * from stus where isDelete=0 and gender=1 order by id desc;
4.4 分页
语法
select * from 表 limit start,count;从start开始，获取count条数据，start索引从0开始
select * from stus where isDelete=0 limit 1,3;
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每页显示m条数据，当前是n页，n从1开始
select * from stus where idDelete=0 limit (n-1)*m,m;