sql中的sum語句

Question

=======================================
Flight   SeatType   Price   GrandTotal
=======================================
F36712   Business   $480
         Economy    $375
         First      $450       ?

F12314   Business   $100
         Economy    $200
         First      $300       ?

我試過這個SQL：

$sql = "SELECT FlightID,SeatType, sum(SeatPrice)Total
                  FROM seat 
                  WHERE SeatAvailable = 'Yes'
                  GROUP BY FlightID,SeatType, SeatPrice";

我能否知道如何計算總計（每次航班的業務，經濟和頭等艙的總和）？

Answer 1

您的查詢版本在group by SeatPrice中具有SeatPrice 。 這意味着您將獲得每個座位價格的單獨一行。 我假設您想獲取每個SeatType組的SeatType ：

SELECT FlightID,SeatType, sum(SeatPrice) as Total
FROM seat 
WHERE SeatAvailable = 'Yes'
GROUP BY FlightID, SeatType with rollup;

但是，這並未將總計放在單獨的列中。 再次，大多數版本的SQL支持窗口都可以執行此操作：

SELECT FlightID,SeatType, sum(SeatPrice) as Total,
       sum(sum(SeatPrice)) over (partition by FlightId)
FROM seat 
WHERE SeatAvailable = 'Yes'
GROUP BY FlightID, SeatType;

編輯：

MySQL不支持窗口功能。 您可以對聯接和聚合執行相同的操作：

SELECT s.FlightID, s.SeatType, sum(s.SeatPrice) as Total, f.GrandTotal
FROM seat s join
     (select FlightId, sum(SeatPrice) as GrandTotal
      from seat
      where SeatAvailable = 'Yes'
      group by FlightId
     ) f
     on s.FlightId = f.FlightId
WHERE s.SeatAvailable = 'Yes'
GROUP BY s.FlightID, s.SeatType;

Answer 2

既然如此，您需要將GrandTotal設為您無法在GROUP BY中使用SeatType的每個航班的所有商務，經濟艙和頭等艙座位的總和。

$sql = "SELECT FlightID, SUM(SeatPrice) AS Total
        FROM seat 
        WHERE SeatAvailable = 'Yes'
        GROUP BY FlightID";