计算MySQL select语句的最大值之和

Question

Reading through similar threads, but I cannot find a reason as to why this isn't working:

select sum(max(i.invoice_total)) as 'Sum of Largest Unpaid Invoice'
from (select vendor_id, MAX(invoice_total)
from vendors v join invoices i using (vendor_id)
where i.payment_date is null
group by v.vendor_id) as alias;

Shouldn't this calculate the sum of the maximum invoice_total? Keeps giving me 'unknown column' error when I add the sum in front of the max.

Answer 1

You need to name the column . . . I would do so explicitly:

select sum(max_invoice_total) as `Sum of Largest Unpaid Invoice`
from (select vendor_id, MAX(invoice_total) as max_invoice_total
      from vendors v join
           invoices i
           using (vendor_id)
      where i.payment_date is null
      group by v.vendor_id
     ) alias;

Answer 2

Try this- give max(invoice_total) an alias and then use that in the outer select:

select sum(max_invoice) as 'Sum of Largest Unpaid Invoice'
from (select vendor_id, MAX(invoice_total) as max_invoice
from vendors v join invoices i using (vendor_id)
where i.payment_date is null
group by v.vendor_id) as alias;