*조인
- 두 개 이상의 테이블을 사용해서 데이터를 조회하는 것.

create table member(
	id varchar(20) not null primary key,
	name varchar(50) not null,
	email varchar(20) not null
)

insert into member values('hkd','hongkildong','hkd@gmail.com');
insert into member values('lss','leesoonsin','lss@gmail.com');
insert into member values('wg','wanggun','wg@gmail.com');

select * from member;

*참조키 또는 외래키 foreign key
=> 참조하는 컬럼의 값만 사용할 수 있도록 강제함.
create table orders(
	orderNumber int not null primary key,
	id varchar(20) not null,
	orderDate char(8) not null,
	foreign key (id) references member(id)
)

-- member에 없는 id값 sj는 입력불가. 참조키가 입력을 제한함.
insert into orders value( 20160001,'sj','20160616');

주문테이블에서 회원명, 주문번호, 주문날짜 출력.

1)표준 ANSI SQL문법
select member.name, orders.orderNumber, orders.orderDate
from member join orders
on member.id=orders.id
where orderDate>'20151231';

2)비표준 문법. 사실상 표준.
select member.name, orders.orderNumber, orders.orderDate
from member , orders
where member.id=orders.id and orderDate>'20151231';

select m.name, o.orderNumber, o.orderDate
from member m , orders o
where m.id=o.id and orderDate>'20151231';

*집계함수
create table goods(
	goodsNumber char(8) not null primary key,
	price int not null
)
insert into goods values('f0000001',10000);
insert into goods values('f0000002',20000);
insert into goods values('e0000003',100000);

select max(price) as 최대값 from orders; -- 최대값
select min(price) from orders; -- 최소값
select avg(price) from goods; -- 평균값
select sum(price) from goods; -- 합계
select count(*) from goods; -- 갯수