SQL Server 2022

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CREATE TABLE Invoice (
  Id        VARCHAR(3) PRIMARY KEY,
  Pax       INT NOT NULL
)

CREATE TABLE InvoiceLine (
  Id        VARCHAR(3) PRIMARY KEY,
  InvoiceId VARCHAR(3) NOT NULL,
  Activity  VARCHAR(80) NOT NULL,
  Amount    DECIMAL(19,4) NOT NULL,
  CONSTRAINT FK_InvoiceLine_InvoiceId FOREIGN KEY (InvoiceId) REFERENCES Invoice (Id)
)
    INSERT INTO Invoice VALUES ('001', 2);
    INSERT INTO Invoice VALUES ('002', 2);
    INSERT INTO Invoice VALUES ('003', 4);
    INSERT INTO InvoiceLine VALUES ('001', '001', 'Ticketing',   40);
    INSERT INTO InvoiceLine VALUES ('002', '001', 'Reservation', 10);
    INSERT INTO InvoiceLine VALUES ('003', '002', 'Ticketing',   30);
    INSERT INTO InvoiceLine VALUES ('004', '002', 'Ticketing',   30);
    INSERT INTO InvoiceLine VALUES ('005', '002', 'Reservation',  8);
    INSERT INTO InvoiceLine VALUES ('006', '002', 'Insurance',    6.6);
    INSERT INTO InvoiceLine VALUES ('007', '003', 'Ticketing',  120);
    INSERT INTO InvoiceLine VALUES ('008', '003', 'Ticketing',   40);
11 rows affected

WITH a AS (
    SELECT InvoiceId, COUNT(DISTINCT Activity) AS ActivityCount
    FROM InvoiceLine
    GROUP BY InvoiceId
),
b AS (
    SELECT
        il.Activity,
        SUM(il.Amount) AS Amount,
        i.Pax,
        a.ActivityCount
    FROM Invoice i
    JOIN InvoiceLine il ON i.Id = il.InvoiceId
    JOIN a ON i.Id = a.InvoiceId
    GROUP BY il.Activity, i.Pax, a.ActivityCount
)
SELECT
    Activity,
    SUM(Amount) AS Amount,
    SUM(Pax) AS Pax,
    SUM(CAST(Pax AS FLOAT) / ActivityCount) AS GlobalPax
FROM b
GROUP BY Activity


Activity
Amount
Pax
GlobalPax


Insurance
6.6000
2
0.666666666666667

Reservation
18.0000
4
1.66666666666667

Ticketing
260.0000
8
5.66666666666667

Activity	Amount	Pax	GlobalPax
Insurance	6.6000	2	0.666666666666667
Reservation	18.0000	4	1.66666666666667
Ticketing	260.0000	8	5.66666666666667