Question

我有这个代码

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

给出

的输出

Click to View output

我的问题是如何让买家专栏由具有相同书籍的逗号分隔。

Answer 1

使用GROUP_CONCAT函数，但这意味着必须用GROUP BY替换DISTINCT：

    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

后续问题，我可以对用户ID进行排序吗？

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会占用您的用户ID并将它们连接起来。试试这个。

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

MySQL查询：最佳查询

2 个答案: