如何分組並統計在一行中？

Question

爲了簡化，我有樹表：products，products-vs-orders，orders

1. products字段： '產品ID'， '姓名'， 'isGratis'，...
2. products-vs-orders字段： '產品ID'，「訂單ID」
3. orders字段： '訂單ID'， '標題'，...

其實，我有這樣的查詢：

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` 

這個查詢工作，並返回這個需要收費的結果：

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

我怎樣才能到單獨的cols檢索產品「免費」和「支付」的計數？

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

Answer 1

試試這個：

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

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

Answer 3

這應該是更合適的標準的SQL：

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