子查询

1.分类表
create table category(
cid varchar(32) primary key,
cname varchar(100)
); 

2.商品表
create table product(
pid varchar(32) primary key,
pname varchar(40),
price double,
category_id varchar(32)
);

4.
insert into category(cid,cname) values('c001','家电');
insert into category(cid,cname) values('c002','服饰');
insert into category(cid,cname) values('c003','化妆品');

 

5.

insert into product(pid,pname,price,category_id) values('p001','联想','5000','c001');

insert into product(pid,pname,price,category_id) values('p002','海尔','5000','c001');
insert into product(pid,pname,price,category_id) values('p003','雷神','5000','c001');

insert into product(pid,pname,price,category_id) values('p004','JACK JONES','800','c002');
insert into product(pid,pname,price,category_id) values('p005','真维斯','200','c002');
insert into product(pid,pname,price,category_id) values('p006','花花公子','440','c002');
insert into product(pid,pname,price,category_id) values('p007','劲霸','2000','c002');

insert into product(pid,pname,price,category_id) values('p008','香奈儿','800','c003');
insert into product(pid,pname,price,category_id) values('p009','相宜本草','200','c003');

1.查询“化妆品”分类上架商品详情

第一步:隐式内连接：

 select cid from category where cname='化妆品';

最后：

select * from product where category_id=(select cid from category where cname='化妆品');