MYSQL 怎麼 LEFT JOIN 多表聯查

三表聯查

        SELECT 
        a.id,
        a.title,
        a.author,
        a.content,
        a.cover,
        a.category_id,
        a.browse,
        a.created_at,
        b.name AS category_name,
        b.id AS category_id,
        COUNT(c.article_id) AS comments_sum
        FROM article a 
        LEFT JOIN category b ON a.category_id = b.id
        LEFT JOIN comments c ON a.id = c.article_id
        GROUP BY a.id
        ORDER BY a.created_at DESC
        LIMIT (1-1) * 10, 10;   //  1是頁碼  10是每頁條數  最後這一行是分頁

二表聯查

        SELECT
        a.id,
        a.title,
        a.author,
        a.content,
        a.cover,
        a.category_id,
        a.browse,
        a.created_at,
        b.name AS category_name,
        COUNT(c.article_id) AS comments_sum 
        FROM article a
        LEFT JOIN category b ON a.category_id = b.id
        WHERE a.id = id

最好是 LEFT JOIN … NO … 這樣一行一行的寫

參考文章地址
https://blog.csdn.net/wqzbxh/article/details/84400788