如何从一个表中选择两个SUM，但只能从一个表中选择一个SUM。 数据

Question

I have this table

Room       Papers    Pens
1           30        30
3           10        10
4           15        15
4           35        25
3           25        5
2           15        45
2           5         15
4           7         8
4           11        9
4           12        11
1           8         8

I need to get SUM(Papers) for Rooms 2,4 which I know how to get (it will be together 100) but then I need also get in this query SUM(Pens) also for Rooms 2,4 BUT only for highest value for each Room. It will be for Room 2 value 45 and for Room 4 value 25 in this table and SUM must be 70.

I have used this code but ofcourse it is not working correct for Pens value...

SELECT SUM(Papers) AS Papers, SUM(DISTINCT Pens) AS Pens FROM MyTable
WHERE (Room = '2' OR Room = '4')

THX for help

Answer 1

You can do it with conditional aggregation:

SELECT 
  SUM(Papers) AS Papers, 
  SUM(
    CASE 
      WHEN EXISTS (
        SELECT 1 FROM MyTable 
        WHERE Room = m.Room AND Pens > m.Pens 
      ) THEN 0 
      ELSE Pens 
    END 
  ) AS Pens
  FROM MyTable m
WHERE (Room = '2' OR Room = '4')