Question

为了简化，我有树表：products，products-vs-orders，orders

products字段：'ProductID'，'名称'，'isGratis'，...
products-vs-orders字段：'ProductID'，'OrderID'
orders字段：'OrderID'，'标题'，...

实际上，我有这样的查询：

SELECT orders.OrderID, orders.Title, COUNT(`products`.`isGratis`) AS "Quantity", `products`.`isGratis`
FROM `orders`, `products-vs-orders`, `products`
WHERE `orders`.`OrderID` = `products-vs-orders`.`OrderID` AND `products-vs-orders`.`ProductID` = `products`.`ProductID`
GROUP BY `products`.`PackID`, `products`.`isGratis`

此查询有效并返回结果：

OrderID,    Title,      Quantity,   isGratis
1            My Order      20           0
1            My Order      3            1
2            An other      8            0
2            An other      1            1

如何检索产品“免费”和“付费”的数量到单独的cols？

OrderID,    Title,      Qt Paid,        Qt Gratis
1            My Order       20              3
2            An other       8               1

Answer 1

试试这个：

SELECT
    orders.OrderID,
    orders.Title, 
    COUNT(orders.OrderId) - SUM(`products`.`isGratis`) AS "Qt Paid", 
    SUM(`products`.`isGratis`) AS "Qt Gratis" 
WHERE `orders`.`OrderID` = `products-vs-orders`.`OrderID`
  AND `products-vs-orders`.`ProductID` = `products`.`ProductID`
GROUP BY `products`.`PackID`

Answer 2

SUM(products.isGratis)取决于布尔值在内部由数据库表示为单个数字位的事实，因此false = 0且true = 1.

在所有数据库实现中可能不是这种情况。因此，布尔字段上的SUM可能会导致依赖于实现的行为。

在求和之前将布尔值转换为实际的0和1值应该更合适：

SELECT orders.OrderID, orders.Title, 
  SUM(CASE WHEN products.isGratis THEN 0 ELSE 1 END) AS "Qt Paid",
  SUM(CASE WHEN products.isGratis THEN 1 ELSE 0 END) AS "Qt Gratis"
FROM orders INNER JOIN `products-vs-orders` ON (orders.OrderID = `products-vs-orders`.OrderID)
  INNER JOIN products ON (`products-vs-orders`.ProductID = products.ProductID)
GROUP BY orders.OrderID, orders.Title

Answer 3

select orderid,title,sum(if(isgratis=0,quantity,0)) as paid,sum(if(isgratis=1,quantity,0)) as gratis from ...

如何分组和统计？

3 个答案: