ROLLUP 返回不正确的值

Question

今天坚持了一会儿，想知道任何人都可以提出问题所在。这是我的代码：

select g.game_name, r.rental_id, sum(if(datediff(r.return_date, r.due_date) > 0, datediff(r.return_date, r.due_date) * g.overdue_charge_per_day, 0)) Overdue_Charges
from rental as r
left join game as g
on r.game_id = g.game_id
where month(r.return_date)=month(now())
group by rental_id
with rollup;

这会显示以下内容：

侠盗猎车手 12 4.00

托尼霍克 13 15.00

Tony Hawk 空 19.00

所以总共是 4 和 15。但是我不希望它显示 "Tony Hawk" 两次。我可以用总计代替吗？也许这是一个加入问题，第二个托尼霍克也应该是空的。谢谢

Answer 1

此行为在文档的 "GROUP BY Modifiers" 部分进行了解释：

MySQL permits a column that does not appear in the GROUP BY list to be named in the select list. In this case, the server is free to choose any value from this nonaggregated column in summary rows, and this includes the extra rows added by WITH ROLLUP. For example, in the following query, country is a nonaggregated column that does not appear in the GROUP BY list and values chosen for this column are indeterminate:
mysql> SELECT year, country, SUM(profit)
    -> FROM sales GROUP BY year WITH ROLLUP;
+------+---------+-------------+
| year | country | SUM(profit) |
+------+---------+-------------+
| 2000 | India   |        4525 |
| 2001 | USA     |        3010 |
| NULL | USA     |        7535 |
+------+---------+-------------+
This behavior occurs if the ONLY_FULL_GROUP_BY SQL mode is not enabled. If that mode is enabled, the server rejects the query as illegal because country is not listed in the GROUP BY clause.

现在，要显示另一个值 "Grand Total"，您可以使用带有 if 的包装查询，如下所示：

select    if(rental_id is null, 'Grand Total', game_name) game_name,
          rental_id,
          Overdue_Charges
from      ( 
        select    game_name 
                  r.rental_id, 
                  sum(if(datediff(r.return_date, r.due_date) > 0, 
                         datediff(r.return_date, r.due_date) * g.overdue_charge_per_day,
                         0)) Overdue_Charges
        from      rental as r
        left join game as g
               on r.game_id = g.game_id
        where     month(r.return_date)=month(now())
        group by  rental_id
        with rollup) sub;

ROLLUP 返回不正确的值

ROLLUP returning incorrect value

mysql

rollup