MySQL查詢：最佳查詢

Question

我有這個代碼

SELECT DISTINCT idx_campus_bookinfo,c.userid as Buyer,bookname,book_explain,writedate
FROM campus_bookinfo cb 
LEFT JOIN user_books ub ON idx_campus_bookinfo = id_product
LEFT JOIN customer c ON ub.id_customer = c.id_customer
where cb.idx_campus = 1 and cb.idxuser = 29 ORDER BY writedate DESC

給出的輸出

點擊查看輸出

我的問題是，如何使買家專欄用同一本書的逗號分隔。

Answer 1

使用GROUP_CONCAT函數，但這意味着必須將DISTINCT替換為GROUP BY：

    SELECT idx_campus_bookinfo,
           GROUP_CONCAT(c.userid SEPARATOR ',') as Buyer,
           bookname,
           book_explain,
           writedate
      FROM campus_bookinfo cb 
LEFT JOIN user_books ub ON idx_campus_bookinfo = id_product
LEFT JOIN customer c ON ub.id_customer = c.id_customer
    WHERE cb.idx_campus = 1 
      AND cb.idxuser = 29 
 GROUP BY idx_campus_bookinfo, bookname, book_explain, writedate
 ORDER BY writedate DESC

后續問題，我可以對用戶名進行排序嗎？

是的你可以：

    SELECT idx_campus_bookinfo,
           GROUP_CONCAT(c.userid ORDER BY c.userid ASC SEPARATOR ',') as Buyer,
           bookname,
           book_explain,
           writedate
      FROM campus_bookinfo cb 
LEFT JOIN user_books ub ON idx_campus_bookinfo = id_product
LEFT JOIN customer c ON ub.id_customer = c.id_customer
    WHERE cb.idx_campus = 1 
      AND cb.idxuser = 29 
 GROUP BY idx_campus_bookinfo, bookname, book_explain, writedate
 ORDER BY writedate DESC

Answer 2

GROUP_CONCAT將獲取您的用戶ID並將其連接起來。 試試看

SELECT idx_campus_bookinfo,
       GROUP_CONCAT(c.userid) as Buyer, bookname, book_explain, writedate
FROM campus_bookinfo cb 
LEFT JOIN user_books ub ON idx_campus_bookinfo = id_product
LEFT JOIN customer c ON ub.id_customer = c.id_customer
WHERE cb.idx_campus = 1 and cb.idxuser = 29
GROUP BY idx_campus_bookinfo
ORDER BY writedate DESC