Main query (Outer query)
Subquery(Inner query) - i)Uncorrelated SQ
Correlated SQ
「Single-row comparison operator
ii)Single-row SQ =Scalar SQ
Multiple-row SQ
∠multiple-row 비교연잔자
iii)Single-column SQ =Scalar SQ
Multiple-column SQ
※지연이 왈 ~~회사에서 서브쿼리가 중요하다고 잘 알아두라고 함.
※강사 왈~~~(안되겠음 이렇게 외워라~~~~)
ANY() ≡ IN()
<ANY
=>less than the maximum
>ANY
=>more tha the minimum
<>ALL
≡NOT IN
# Subquery란?
또 다른 select 문에 포함된 select 문.
# 서브쿼리를 이용한 문제 해결
예) Who has a salary greater than Abel's?
=> Mainquery: Which employees have salaries greater than Abel's salary(subquery)?
Subquery: What is Abel's salary?
select last_name, salary
from employees
where salary > [Abel's salary];
+
select last_name, salary
from employees
where last_name = 'Abel';
↓ ↓ ↓
select last_name, salary
from employees
where salary > (select salary
from employees
where last_name = 'Abel');
↓ ↓ ↓
select last_name, salary
from employees
where salary > 11000;
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