⭐Back-end

SQL

Inner Join

-- 1. MEMBER의 NICNAME과 NOTICE의 WRITER_ID를 엮어서 두 테이블을 조인
SELECT * FROM 
MEMBER INNER JOIN NOTICE ON MEMBER.NICNAME = NOTICE.WRITER_ID; 

Outer Join

SELECT * FROM
MEMBER LEFT JOIN NOTICE ON MEMBER.NICNAME = NOTICE.WRITER_ID;
-- 조인된 레코드의 개수는? 6개

SELECT * FROM
MEMBER RIGHT JOIN NOTICE ON MEMBER.NICNAME = NOTICE.WRITER_ID;
-- 조인된 레코드의 개수는? 5개

SELECT * FROM
MEMBER LEFT JOIN NOTICE ON MEMBER.NICNAME = NOTICE.WRITER_ID;
-- 조인된 레코드의 개수는? 8개

3つのテーブルを接続

NOTICE、MEMBER、COMMENTテーブルの結合

 NOTICE N 
    LEFT JOIN MEMBER M ON N.WRITER_ID = M.NICNAME -- NOTICE, MEMBER 테이블 조인
    LEFT JOIN "COMMENT" C ON N.ID = C.NOTICE_ID -- NOTICE, COMMENT 테이블 조인

例)NOTICE、MEMBER、COMMENTテーブルのチェックインによる投稿数の取得

SELECT N.ID, N.TITLE, N.WRITER_ID, M.NAME WRITER_NAME, COUNT(C.ID) CMT_COUNT 
FROM 
    NOTICE N 
    LEFT JOIN MEMBER M ON N.WRITER_ID = M.NICNAME
    LEFT JOIN "COMMENT" C ON N.ID = C.NOTICE_ID
GROUP BY N.ID, N.TITLE, N.WRITER_ID, M.NAME;

⭐Front-end

JavaScript - ES6

Binary and Octal Literals

let

変数を宣言しないと変数は使用できません.

変数宣言時に自動的にwindowのプロパティにはなりません.

変数を繰り返し宣言することはできません.

領域変数としてカッコブロックを使用します.

const

JSON対象表示法

🐥마무리