5.4 DISTINCT 처리

5.4.1 SELECT DISTINCT

• 1. 정렬이 보장되지 않음.
• 2. 레코드(튜플)를 유니크 하게 함.

5.4.2 집합 함수와 함께 사용된 DISTINCT

• SQL 예시

SELECT DISTINCT first_name, last_name
  FROM employees A
 WHERE 1=1
   AND A.emp_no BETWEEN 10001 AND 10200
;
-- 목록나옴

SELECT COUNT(DISTINCT first_name), COUNT(DISTINCT last_name)
  FROM employees A
 WHERE 1=1
   AND A.emp_no BETWEEN 10001 AND 10200
;
--188 184

SELECT COUNT(DISTINCT A.first_name, A.last_name)
  FROM employees A
 WHERE 1=1
   AND A.emp_no BETWEEN 10001 AND 10200
;
--200