create database if not exists test1;
create table if not exists product(
id int primary key auto_increment,
name varchar(20) not null,
price double,
classify varchar(10)
);
insert into product values(null,'',5000,'001');
insert into product values(null,'',4300,'001');
insert into product values(null,'',3000,'001');
insert into product values(null,'',1000,'002');
insert into product values(null,'',430,'002');
insert into product values(null,'',300,'002');
insert into product values(null,'',2000,'003');
insert into product values(null,'',100,'003');
select price*1.1 as new_price as p from product;
--查询价格不为500的数据
select * from product where price = 500 ;
select * from product where price != 500;
select * from product where price <> 500;
select * from product where not(price = 500);
--查询价格在500-1000之间的数据
select * from product where price between 3000 and 5000;
select * from prodcut where price >= 3000 and price <= 5000;
select * from product where price >= 3000 && price <= 5000;
--查询价格为100和300之间商品
select * from product where price =100 or price = 300;
select * from product where price =100 || price = 300;
select * from product where price in (100,300);
--查询包含海的数据
select * from product where name like '%海%'; --%：匹配任意字符
--查询以海开头的数据
select * from product where name like '海%';
select * from product where name like '%公子';
select * from product where name like '_%';
select * from product where name like '__';
--查询分类为空的字段
select * from product where classify is null;
select * from product where classify is not null;
--使用least求最小值
select least(1,5,10,20) small_num;
select greatest(1,5,10,20) big_num;
select least(1,5,10,20) as small_num;
--如果求最小值是有个值为null,则不会进行比较,结果直接为null
--使用greatest来求最大值
select greatest(1,5,10,20) as big_num;
select least(1,5,10,20,null) small_num;
select greatest(1,5,10,20,null) big_num;
--如果求最大值时，有个值为null,则不会进行比较,结果直接为null
--对查询出来的结果进行排序，默认时升序 asc:升序 desc:降序
--排序关键词 order by
--使用价格进行排序
select * from product order by price;
select * from product order by price desc;
--在价格降序的同时，通过分类排序（降序）
select * from product order by price desc,classify desc;
--聚合函数：对表里的每一个数据进行计算
--count（）：统计：count() 求和:sum() 最大值:max() 最小值:min() 平均值:avg()
--聚合查询：
--1：统计表里一共有多少条数据
select count(id) from product;
select count(id) as '总数' from product;
select count() as '总数' from product;
select count(classify) as '总数' from product;
--2：查询所有的数据，满足价格大于500的
select count () as '总数' from product where price >= 500;
--3：对表里商品进行求和
select sum(price) from product;
select sum(price) from product where classify = 'c001';
--5：最大值
select max(price) from product;
--6：最小值
select min(price) from product;
--7：求和 最大值 最小值
select max(price) max_price,min(price) min_price,sum(price) from product;
--8：求所有价格的平均值
select avg(price) from product;
select avg(price) from prodcut where classify = 'c001';
--分组查询：对查询的信息进行分组
select classify, count() from product group by classify;
select classify ,count() from product group by classify having count() > 5
select
classify ,count()
from
product
group by
classify
having count(*) > 5;
select * from product limit 5;
select * from product limit 0,5;
select * from product limit 3,5;
select * from product limit 5,5;
select * from product limit 10,5;
drop table product;
create table tset_null(
c1 varchar(5),
c2 double
);
insert into test_null(name,price) select name,price from probuct
--查看聚合函数对于null的处理
create table test_null1(
c1 varchar(5),
c2 INT
);
insert into test_null1 values('aaa',10);
insert into test_null1 values('bbb',200);
insert into test_null1 values('ccc',null);
select count() from test_null1;
select count(),count(c2) from test_null1
select max(c2),min(c2),avg(c2),sum(c2) from test_null1;