union, union all, intersect, except

--UNION 연산자 (컬럼의 갯수만 맞으면 됨)

select C.custId, C.custName, G.goodsName 
from customersTbl C 
inner join salesTbl S ON C.custId = S.custId 
inner join goodsTbl G On S.goodsId = g.goodsId 
where C.custId='kkkkkkkk' 

--union  
--union all 
--union all은 중복데이터를 걸러주지 않음 
--intersect 
--intersect는 교집합을 의미(inner) 
--except 
--except는 차집합을 의미한다(outer) 

select C.custId, C.custName, G.goodsName 
from customersTbl C 
inner join salesTbl S ON C.custId = S.custId 
inner join goodsTbl G ON S.goodsId = G.goodsId 
where G.goodsName = '몽쉘';