Question

我有这个问题：

CREATE VIEW MOSTACTIVESELLER AS
Select a.* from
(
SELECT a.ownerID, b.sellerName, count(distinct a.ITEMID) as item_qty
FROM item AS a
INNER JOIN seller AS b ON a.ownerID = b.sellerID
GROUP BY a.ownerID,b.sellerName 
) a

此视图查询的结果是：

+--ID--+--seller-+-qty--+
| 1000 | Nick     | 3 |
| 1001 | Morgan   | 2 |
| 1002 | stancly  | 1 |
| 1003 | chandler | 1 |
| 1004 | chiptle  | 3 |
| 1005 | samir    | 2 |
| 1006 | matuidi  | 3 |
| 1007 | medjek   | 1 |
| 1008 | leo      | 1 |
| 1009 | georgi   | 1 |
| 1010 | bocheli  | 2 |
+------+----------+---+

所以我想要的是使用像max这样的聚合函数来仅返回此列表中最活跃的卖家（仅1），因为你可以看到3个卖家有数量3，我认为max函数将返回一个。如果不是我可能会订购视图DESC并返回最高值。但无法使其发挥作用。我尝试使用max与视图MOSTACTIVESELLER我不知道该怎么做??

Answer 1

我很惊讶你的查询在MySQL中运行 - 通常在视图的FROM子句中不允许子查询。但这应该是一种观点：

CREATE VIEW MOSTACTIVESELLER AS
    SELECT s.sellerID, s.sellerName, count(distinct i.ITEMID) as item_qty
    FROM item i INNER JOIN
         seller s
         ON i.ownerID = s.sellerID
    GROUP BY s.sellerID, s.sellerName 
    HAVING count(distinct i.ITEMID) = (SELECT count(distinct i.ITEMID)
                                       FROM item i
                                       GROUP BY i.ownerID
                                       ORDER BY 1 DESC
                                       LIMIT 1
                                      );

编辑：

我认为LIMIT允许使用=，但MySQL对子查询中LIMIT的使用有奇怪的限制。这很容易取代：

    HAVING count(distinct i.ITEMID) >= ALL (SELECT count(distinct i.ITEMID)
                                            FROM item i
                                            GROUP BY i.ownerID
                                           );

MAX汇总功能与VIEW

1 个答案: