选择具有唯一值的行数

Question

我有一张桌子，里面有我们卖的所有物品。 订单中可能有多个商品。

我想找到最受欢迎的项目颜色组合，其中订单仅包含1个项目。 我想知道是否可以在一个MySQL语句中找到它（可能使用嵌套的Selects）。 到目前为止，我已经尝试了几件事但没有成功。

ProductName | Color | OrderNum | 
--------------------------------
productA    | black | 1
productA    | black | 1
productA    | black | 2
productA    | black | 3
productA    | black | 4
productA    | black | 4
productA    | black | 5

所以“

SELECT COUNT(ProductName), ProductName WHERE ~~COUNT(OrderNum)=1~~ GROUP BY ProductName, Color

会显示：

COUNT(ProductName) | ProductName | Color
      3            | ProductA    | black

实际上我有很多产品和50多种颜色。

我尝试过的：

SELECT COUNT(ProductName), ProductName,Color, 
       (SELECT COUNT(OrderNum) FROM Items GROUP BY OrderNum) AS itemcount 
FROM Items WHERE 1 
GROUP BY ProductName,Color HAVING itemcount = 1

SELECT COUNT( ProductName ) , ProductName, Color
FROM Items
WHERE (SELECT COUNT( OrderNum ) AS itemcounts
       FROM Items GROUP BY OrderNum
) =1
GROUP BY ProductName

- “子查询返回超过1行”

谢谢你的帮助。

Answer 1

查询：

SQLFIDDLEExample

SELECT
COUNT(*) as count, i.ProductName, i.Color
FROM ITems i
WHERE 1 = (SELECT COUNT( OrderNum ) AS itemcounts
           FROM Items 
           WHERE OrderNum = i.OrderNum
           )
GROUP BY ProductName, Color

结果：

| COUNT | PRODUCTNAME | COLOR |
-------------------------------
|     3 |    productA | black |

Answer 2

尝试这个：

SELECT ProductName, color, COUNT(ProductName) 
FROM (SELECT ProductName, color, orderNum FROM Items 
      GROUP BY ProductName, orderNum HAVING COUNT(orderNum)=1) AS A