EXPLAIN 결과 컬럼

id: 행이 속한 SELECT 구분자 UNION이나 서브쿼리가 없으면 하나의 SELECT만 존재하여 모든 행의 id=1 Derived Table or Subquery will have different ‘id’ values
select_type: SELECT 쿼리타입 구분 Simple or Complex -Simple 서브쿼리나 UNION 없음 -Complex 1. Simple subqueries 2. Derived tables 3. UNIONs(id = null)

EXPLAIN SELECT (SELECT 1 FROM sakila.actor LIMIT 1) FROM sakila.film;

id	select_type	table
1	PRIMARY	film
2	SUBQUERY	actor

EXPLAIN SELECT film_id FROM (SELECT film_id FROM sakila.film) AS der;

id	select_type	table
1	PRIMARY	`<derived2>`
2	DERIVED	film

EXPLAIN SELECT 1 UNION ALL SELECT 1;