SQL Joins Tutorial 정보
SQL Joins Tutorial본문
필요한 데이타베이스 만들기
create database sqljoins;
커스터머 데이타
create table sqljoins.customer
(
CustomerID int,
CityID int,
CustomerName varchar(50)
);
insert into sqljoins.customer (CustomerID, CityID, CustomerName) values (1, 1, 'Bob Smith');
insert into sqljoins.customer (CustomerID, CityID, CustomerName) values (2, 1, 'Sally Smith');
insert into sqljoins.customer (CustomerID, CityID, CustomerName) values (3, 2, 'Tom Smith');
insert into sqljoins.customer (CustomerID, CityID, CustomerName) values (4, NULL, 'Mary Smith');
시티 데이타
create table sqljoins.city
(
CityID int,
CityName varchar(50)
);
insert into sqljoins.city (CityID, CityName) values (1, 'Kansas City');
insert into sqljoins.city (CityID, CityName) values (2, 'New York');
insert into sqljoins.city (CityID, CityName) values (3, 'Houston');
제대로 들어가있는지 체크
select * from sqljoins.Customer;
select * from sqljoins.City;
inner조인
select * from sqljoins.customer
inner join sqljoins.city on customer.cityid=city.cityid;
레프트 조인
select * from sqljoins.customer
left join sqljoins.city on customer.cityid=city.cityid;
라이트 조인
select * from sqljoins.customer
right join sqljoins.city on customer.cityid=city.cityid;
위와 같은 내용 즉 레프트 조인만 잘 알면 됨.
select * from sqljoins.city
left join sqljoins.customer on customer.cityid=city.cityid;
풀 조인은 mysql에 명령어가 없습니다. 아래와 같이 union으로 처리한다고 합니다.
select * from sqljoins.customer
left join sqljoins.city on customer.cityid=city.cityid
union
select * from sqljoins.customer
right join sqljoins.city on customer.cityid=city.cityid;
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