sql中的sum语句

Question

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

F12314   Business   $100
         Economy    $200
         First      $300       ?

I've tried this SQL:

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

May I know how can I calculate the grand total (sum of the business, economy and first class for each flight)?

Answer 1

Your version of the query has SeatPrice in the group by . This means that you are getting a separate row for each seat price. I assume you want to get the total in each group of SeatType :

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

However, that does not put the grand total in a separate column. Once again, most versions of SQL support window functions to do this:

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

EDIT:

MySQL does not support window functions. You can do the same with a join and aggregation:

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

Since, you need the GrandTotal to be the Sum of all the business, economy and first class seats for each flight you can't have SeatType in the GROUP BY.

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