MySQL SUM function in multiple joins

Question

Hi so this is my case I have those tables

Customer {id,name}
Charges {id,amount,customer_id}
Taxes {id,amount,charge_id}

so I want to SUM amoun

Answer 1

This is a pain because of the multiple hierarchies. I would suggest:

SELECT c.id, ch.charge_amount, ch.taxes_amount
FROM Customer c LEFT JOIN
     (SELECT ch.customer_id, SUM(ch.amount) as charge_amount,
             SUM(t.taxes_amount) as taxes_amount
      FROM Charges ch LEFT JOIN
           (SELECT t.charge_id, SUM(t.amounts) as taxes_amount
            FROM taxes t
            GROUP BY t.charge_id
           ) t
           ON t.charge_id = ch.id
      GROUP BY ch.customer_id
     ) ch
     ON ch.customer_id = c.id;

You are not going to be able to fix this without subqueries of one form or another, if there are multiple charges for a customer or multiple taxes on a charge.

Answer 2

You want to know if you can do this without subqueries. No, you can't.

If a row in Charges has more than one corresponding row in Taxes, you can't simply join the tables without duplicating Charges rows. Then, as you have discovered, when you sum them up, you'll get multiple copies.

You need a way to get a virtual table (a subquery) with one row for each Charge.

                    SELECT ch.customer_id,
                           ch.amount amount,
                           tx.tax tax
                      FROM Charges
                      LEFT JOIN (  
                                  SELECT SUM(amount) tax,
                                         charge_id 
                                    FROM Taxes
                                   GROUP BY charge_id
                          ) tx ON ch.id = tx.charge_id

You can then join that subquery to your Customer table to summarize sales by customer.