Ordering search of joined tables in 2 ways - php

Question

I am trying to search for the oldest outstanding invoice for each customer and then present the results in descending order of that invoice date however the result gives me the date of the most recent invoice. How can I ensure that it picks up the earliest invoice date? Many thanks in advance.
Here is my query:
$checkDebtors = "select
a.accountNumber as accountNumber, a.balanceOutstanding as balanceOutstanding, a.companyName as companyName, b.invoiceDate as invoiceDate, b.netOutstanding as netOutstanding
from
customersQQuote a
Right JOIN invoices b ON a.accountNumber = b.accountNumber
WHERE netOutstanding > 0 AND balanceOutstanding > 0
group by
a.accountNumber
order by
b.invoiceDate ASC";

Answer 1

Did you mean the result by following sql? Try it, if it does not work for you, leave a comment for me;)
select
a.accountNumber as accountNumber,
a.balanceOutstanding as balanceOutstanding,
a.companyName as companyName,
b.invoiceDate as invoiceDate,
c.netOutstanding as netOutstanding
from
(SELECT accountNumber, MIN(invoiceDate) AS invoiceDate FROM invoices GROUP BY accountNumber) b
LEFT JOIN customersQQuote a ON a.accountNumber = b.accountNumber
LEFT JOIN invoices c ON c.accountNumber = b.accountNumber AND c.invoiceDate = b.invoiceDate
WHERE c.netOutstanding > 0 AND a.balanceOutstanding > 0
group by
a.accountNumber
order by
b.invoiceDate ASC

Answer 2

Above code has certain mistakes such as, alias name using in where clause and misuse of group by clause. you can apply this piece of code..
select a.accountNumber as accountNumber, a.balanceOutstanding as balanceOutstanding,
a.companyName as companyName, b.invoiceDate as invoiceDate, b.netOutstanding as netOutstanding
from customersQQuote a Right JOIN invoices b ON a.accountNumber = b.accountNumber
WHERE b.netOutstanding > 0 AND a.balanceOutstanding > 0 order by b.invoiceDate;

Answer 3

Your current code does not work as you have not specified which invoice to pull back. You have used GROUP BY accountNumber, so it will return one row for each accountNumber value. Other fields should be aggregate values (ie, the result of a aggregate function such as MIN() or MAX()). If fields are neither mentioned in the GROUP BY clause nor the result of an aggregate function then MySQL will return a value for that column, but which row that value comes from is not defined. It could be the first or the last rows value, or any in between (and could change between different versions of MySQL).
Most flavours of SQL do not allow a query like this and would error. MySQL has a feature that does allow this. But this feature can be configured to be turned off.
To do this in standard SQL and give you a consistent value you use a sub query to get the first invoiceDate for each accountNumber, using the MIN() aggregate function. Then you join this sub query against the invoices table to get the other columns.
SELECT a.accountNumber,
a.balanceOutstanding,
a.companyName,
b.invoiceDate,
b.netOutstanding
FROM
(
SELECT accountNumber,
MIN(invoiceDate) as invoiceDate
FROM invoices
GROUP BY accountNumber
) sub0
INNER JOIN invoices b ON sub0.account_number = b.account_number AND sub0.invoiceDate = b.invoiceDate
INNER JOIN customersQQuote a ON sub0.account_number = a.account_number
Note that if an accountNumber could have 2 identical first invoiceDate values then you will need to pick another field to minimise (ie, maybe your unique id field) for each date. Gets messy but something like this:-
SELECT a.accountNumber,
a.balanceOutstanding,
a.companyName,
b.invoiceDate,
b.netOutstanding
FROM
(
SELECT accountNumber,
MIN(invoiceDate) as invoiceDate
FROM invoices
GROUP BY accountNumber
) sub0
INNER JOIN
(
SELECT accountNumber,
invoiceDate,
MIN(id) as id
FROM invoices
GROUP BY accountNumber, invoiceDate
) sub1 ON sub0.accountNumber = sub1.accountNumber AND sub0.invoiceDate = sub1.invoiceDate
INNER JOIN invoices b ON sub1.account_number = b.account_number AND sub1.invoiceDate = b.invoiceDate AND sub1.id = b.id
INNER JOIN customersQQuote a ON sub0.account_number = a.account_number

Answer 4

Thank you for your advice. I got some good tips from your answers which helped me solve the problem. The main thing being the use of MIN() and also that I was using Right join rather than Left. Additionally I just used the invoiceDate keyword in the ORDER BY rather than the b.invoiceDate. I guess this ensured the MIN rule was used here as well. Thanks to you I ended up getting the result I needed.
select
a.accountNumber as accountNumber, a.balanceOutstanding as balanceOutstanding, a.companyName as companyName, MIN(b.invoiceDate) as invoiceDate, b.netOutstanding as netOutstanding
from
customersQQuote a
Left JOIN invoices b ON a.accountNumber = b.accountNumber
WHERE netOutstanding > 0 AND balanceOutstanding > 0
group by
a.accountNumber
order by invoiceDate ASC