如何对 MySQL 中的两个表的数学结果求和

Question

Not sure what to do!

Using MySQL

I need to display the total trips per hour a specific operatorID

So the total tripsperhour for operatorid '2' should be displayed as a number '7' somewhere. This number '7' is the sum of TripsPerHour.

SELECT S.routeid, S.operatorid, R.routeid, S.percentage * R.frequency/100 AS TripsPerHour 
  FROM route_split S, routes R 
 WHERE R.routeid = S.routeid
   AND S.operatorid ='2';
+---------+------------+---------+--------------+
| routeid | operatorid | routeid | TripsPerHour |
+---------+------------+---------+--------------+
|       6 |          2 |       6 |       1.0000 |
|      12 |          2 |      12 |       4.0000 |
|      13 |          2 |      13 |       2.0000 |
+---------+------------+---------+--------------+
3 rows in set (0.00 sec)

Answer 1

You just need SUM() aggregation along with GROUP BY clause

SELECT S.operatorid, R.routeid, 
       SUM(S.percentage * R.frequency/100) AS TripsPerHour 
  FROM route_split S
  JOIN routes R 
    ON R.routeid = S.routeid
 GROUP BY S.operatorid, R.routeid

If you only need the value with operatorid=2 , then add

WHERE S.operatorid = 2

before GROUP BY such as

SELECT R.routeid, 
       SUM(S.percentage * R.frequency/100) AS TripsPerHour 
  FROM route_split S
  JOIN routes R 
    ON R.routeid = S.routeid
 WHERE S.operatorid = 2
 GROUP BY R.routeid

Update: you can add SUM() OVER () window function provided that your DB version is 8.0+ such as

SELECT S.operatorid, R.routeid,
       SUM(S.percentage * R.frequency/100) OVER () AS Total_TripsPerHour 
  FROM route_split S
  JOIN routes R 
    ON R.routeid = S.routeid
 WHERE S.operatorid = 2

Answer 2

You could also use the WITH ROLLUP option to get your cumulative sum as a separate row:

         SELECT  S.operatorid, R.routeid, 
       SUM(S.percentage * R.frequency/100) AS TripsPerHour ) FROM
  route_split S JOIN routes R 
    ON R.routeid = S.routeid GROUP BY S.operatorid, R.routeid WITH ROLLUP

Whichever answer you choose, do an EXPLAIN on it before you put it into production.