MySQL不加和不带子查询

Question

I have two main tables bills and billing_items:

bills
_______
id
..
amount
balance

billing_items
______________
id
...
bill_id

I need to get the sum of the bill amount and balance based on certain criteria in the billing_items table (the table references other tables of interest)

when I use the below query I get duplicates:

select sum(b.amount), sum(b.balance) 
from bills b left join billing_items bi 
on b.id=bi.bill_id;

I can't use subqueries such as the one below because of the ORM I'm using (subqueries not supported):

select sum(a) from 
(select b.amount as a, b.balance 
   from bills b left join billing_items bi 
   on b.id=bi.bill_id group by b.id) t;

the criteria on billing_items and its referencing tables is ommited but I need to reference billing_items

Answer 1

not sure if your ORM allows the use of user variables or not in your SQL, if yes you could try this, basically it's ORDER BY bi.bill_id and only sum amount when there's a new bill_id

select sum(IF (@prevBillId IS NULL OR @prevBillId != bi.bill_id,b.amount,0)) as sumAmount, 
       sum(IF (@prevBillId IS NULL OR @prevBillId != bi.bill_id,b.balance,0)) as sumBalance,
       @prevBillId:=bi.bill_id
from bills b left join billing_items bi 
on b.id=bi.bill_id
ORDER BY bi.bill_id;

see this sqlFiddle

Answer 2

Hopefully this will work...

So your issue is your left join to billing_items is causing multiple rows per billing item and your sum(b.amount) is being multiplied by the number of rows you have. So solution...divide your sum by your count.

select b.id,sum(b.amount) / count(*) as amount, sum(b.balance) 
from bills b left join billing_items bi 
on b.id=bi.bill_id;
group by b.id

Give that a try...hoping it works out.