Eliminate database rows based on mod dates - sql

Question

I have an issue grabbing data from two tables base on a single field in one of the tables The field does not exist in both tables.
Example:
Table 1 (call it invoices):
invoice email customer_name original_bill invoice_status
1 a#g.com bob 5.00 P
2 a#g.com harry 23.00 P
3 a#g.com sally 4.00 P
4 b#g.com loretta 14.00 P
5 b#g.com hamish 74.00 P
Table 2 (customer invoice edits):
invoice email date_last_modified_timestamp mod_status mod_amount
1 a#g.com 2019-05-01 A 3.00
1 a#g.com 2019-04-01 D
3 b#g.com 2019-10-25 A
What I want
a list of all invioces and their mods but I only wish each invoice to appear once in the list. based on the latest date in Table two.
example:
invoice email customer_name original_bill invoice_status date_last_modified_timestamp mod_status mod_amount
1 a#g.com bob 5.00 P 2019-05-01 A 3.00
2 a#g.com harry 23.00 P
3 a#g.com sally 4.00 P 2019-10-25 A
4 b#g.com loretta 14.00 P
5 b#g.com hamish 74.00 P
How im pulling it now:
select invoice, email, customer_name, original bill, invoice status, max(date_last_modified_timestamp), mod status, mod_amount
from table one
left join on table1.invoice = table 2.invoice
group by
invoice, email, customer_name, original bill, invoice status, max(date_last_modified_timestamp), mod status, mod_amount
I've tried a gazzillion variation to no avail.
What i get
i do get accurate results, but those results inclues a duplicate row containing each invoice that has been modified. I only want one invoice per row. I want the one that's been modified last. Is this even possible? What am I doing wrong?

Answer 1

You can join and use a correlated subquery for filtering:
select i.*, e.*
from invoices i
inner join customer_invoice_edits e
on e.invoice = i.invoice
and e.date_last_modified_timestamp = (
select max(date_last_modified_timestamp)
from customer_invoice_edits e1
where e1.invoice = e.invoice
)
This will give you one record per row in the invoices table that has a match in customer_invoice_edits, along with the latest corresponding record in customer_invoice_edits.
If some invoices have no corresponding record in the dependant table, they will not appear in the resultset. If you do want to see them, then you can use a left join instead.

Answer 2

Is this what you want?
select
invoice,
email
from (
select
invoice,
email,
mod_status,
mod_amount,
date_last_modified_timestamp,
row_number() over (
partition by invoice, email
order by date_last_modified_timestamp desc
) rn
from table2
)
where rn=1

Answer 3

I'm pretty sure you want this field-by-field. Here is an example:
select i.invoice,
nz( (select top (1)
from invoice_edits as ie
where ie.invoice = i.invoice and ie.email is not null
), i.email
) as email,
nz( (select top (1)
from invoice_edits as ie
where ie.invoice = i.invoice and ie.mod_amount is not null
), i.original_bill
) as original_bill,
. . .
from invoices as i;