Question

请，

我试图在几个不同的计数中获得用户获得积分的总价值，但一切都来自同一张桌子。

SQL：

SELECT o.author_id, SUM(o.vote_value) AS vote_value, n.best AS best_sum, 
                (SUM(o.vote_value) + (10 * n.best)) AS total
                FROM comments o
                LEFT JOIN (
                  SELECT COUNT(best) AS best, author_id
                  FROM comments
                  WHERE best = 1
                  GROUP BY author_id
                  ) n ON o.author_id = n.author_id
                GROUP BY o.author_id
                ORDER BY total DESC
                LIMIT 0, 4

问题是如果没有BEST（默认值为0，最好是1）我没有得到“total”和“best_sum”的任何内容。如果用户没有“最佳”，我需要0才能正确执行计算

对不起，我的英语不好，我想你会明白的感谢

Answer 1

如果最佳= NULL ，请考虑COALESCE

我假设你想要一个0值

count(COALESCE(best,0) AS best)

Answer 2

你应该使用COALESCE（n.best，0）

当第一个参数为NULL时，COALESCE返回第二个参数

SELECT o.author_id, SUM(o.vote_value) AS vote_value, 
            COALESCE(n.best, 0) AS best_sum, 
            (SUM(o.vote_value) + (10 * COALESCE(n.best, 0))) AS total
            FROM comments o
            LEFT JOIN (
              SELECT COUNT(best) AS best, author_id
              FROM comments
              WHERE best = 1
              GROUP BY author_id
              ) n ON o.author_id = n.author_id
            GROUP BY o.author_id
            ORDER BY total DESC
            LIMIT 0, 4

Answer 3

我认为你的问题是你过滤掉了最好不是1的行，所以它们不包含在组中。试试这个：

SELECT o.author_id, SUM(o.vote_value) AS vote_value, n.best AS best_sum, 
            (SUM(o.vote_value) + (10 * n.best)) AS total
            FROM comments o
            JOIN (
              SELECT SUM(best) AS best, author_id
              FROM comments
              GROUP BY author_id
              ) n ON o.author_id = n.author_id
            GROUP BY o.author_id
            ORDER BY total DESC
            LIMIT 0, 4

另外，也许我错过了一些东西，但不会这样做，保存子查询？

SELECT o.author_id, SUM(o.vote_value) AS vote_value, SUM(o.best) AS best_sum, 
            (SUM(o.vote_value) + (10 * SUM(o.best))) AS total
            FROM comments o
            GROUP BY o.author_id
            ORDER BY total DESC
            LIMIT 0, 4

SQL添加问题

3 个答案: