是否可以简化此SQL查询？

Question

我有3张桌子。

'Order details' OrderID | Quantity | UnitPrice | ProductID 1002 | 19 | 17 | 824 1003 | 5 | 15 | 285 1004 | 7 | 6 | 543

'Orders' OrderID | CustomerID 1002 | 224 1003 | 224 1004 | 348

'Customers' CustomerID| Name | Phone 224 | John | 235-453 225 | July | 532-232

我必须获得有关订购超过10种产品且平均价格低于17的人的信息。我这样做了，但我不确定这是否是最佳方法。

SELECT *
FROM customers
WHERE customerid IN
   (SELECT DISTINCT customerid
    FROM orders
    WHERE orderid IN
       (SELECT orderid id
        FROM 'order details'
        WHERE 17 >
            (SELECT avg(unitprice)
             FROM 'order details'
             WHERE orderid = id
             GROUP BY orderid)
          AND 10 <
            (SELECT sum(quantity)
             FROM 'order details'
             WHERE orderid = id
             GROUP BY orderid)
        GROUP BY orderid))

Answer 1

您可以使用"having" clause过滤聚合（总和，计数等）符合特定条件的记录。

这将是：

select customer.Name, 
       count(*), 
       avg(od.unitPrice)
from   customers c
inner join orders o on c.customerID = o.customerID
inner join orderDetails od on o.orderID = od.orderID
group by customer.Name
having count(*) > 10
and avg(od.unitPrice) < 17

Answer 2

尝试这个，不确定它是否可以作为避风港检查过。

SELECT 
  avg(od.unitPrice) AS AVGunitPrice,
  c.Name, 
  c.Phone
FROM Customer c 
  INNER JOIN Orders o ON o.customerID = c.CustomerID
  INNER JOIN OrderDetail od ON od.OrderID = o.OrderId
WHERE od.Quantity > 10
GROUP BY c.Name, c.Phone
HAVING avg(od.unitPrice) < 17