SQL JOIN GROUP BY on three tables to get totals

Question

I ve inherited the following DB design   Tables are   customers --------- customerid   customernumber  invoices -------- invoiceid   amount  invoicepayments --------------- invoicepaymentid   invoiceid   paymentid  payments -------- paymentid   customerid   amount   My query needs to return invoiceid  the invoice amount  in the invoices table   and the amount due  invoice amount minus any payments that have been made towards the invoice  for a given customernumber   A customer may have multiple invoices   The following query gives me duplicate records when multiple payments are made to an invoice   SELECT i invoiceid  i amount  i amount - p amount AS amountdue FROM invoices i LEFT JOIN invoicepayments ip ON i invoiceid   ip invoiceid LEFT JOIN payments p ON ip paymentid   p paymentid LEFT JOIN customers c ON p customerid   c customerid WHERE c customernumber    100    How can I solve this

User · Answer

I have a tip for those  who want to get various aggregated values from the same table    Lets say I have table with users and table with points the users acquire  So the connection between them is 1 N  one user  many points records    Now in the table  points  I also store the information about for what did the user get the points  login  clicking a banner etc    And I want to list all users ordered by SUM points  AND then by SUM points WHERE type   x   That is to say ordered by all the points user has and then by points the user got for a specific action  eg  login    The SQL would be   SELECT SUM points points  AS points all  SUM points points    points type   7   AS points login FROM user LEFT JOIN points ON user id   points user id GROUP BY user id   The beauty of this is in the SUM points points    points type   7   where the inner parenthesis evaluates to either 0 or 1 thus multiplying the given points value by 0 or 1  depending on wheteher it equals to the the type of points we want

User · Answer

I am not sure I got you but this might be what you are looking for   SELECT i invoiceid  sum case when i amount is not null then i amount else 0 end   sum case when i amount is not null then i amount else 0 end  - sum case when p amount is not null then p amount else 0 end  AS amountdue FROM invoices i LEFT JOIN invoicepayments ip ON i invoiceid   ip invoiceid LEFT JOIN payments p ON ip paymentid   p paymentid LEFT JOIN customers c ON p customerid   c customerid WHERE c customernumber    100  GROUP BY i invoiceid   This would get you the amounts sums in case there are multiple payment rows for each invoice

User · Answer

First of all  shouldn t there be a CustomerId in the Invoices table  As it is  You can t perform this query for Invoices that have no payments on them as yet   If there are no payments on an invoice  that invoice will not even show up in the ouput of the query  even though it s an outer join      Also  When a customer makes a payment  how do you know what Invoice to attach it to   If the only way is by the InvoiceId on the stub that arrives with the payment  then you are  perhaps inappropriately  associating Invoices with the customer that paid them  rather than with the customer that ordered them       Sometimes an invoice can be paid by someone other than the customer who ordered the services

User · Answer

I know this is late  but it does answer your original question      Read the comments the same way that SQL runs the query     1  FROM      2  GROUP      3  SELECT      4  My final notes at the bottom     SELECT          list invoiceid         cust customernumber          MAX list inv amount  AS invoice amount   we select the max because it will be the same for each payment to that invoice  presumably invoice amounts do not vary based on payment             MAX list inv amount  - SUM list pay amount   AS  amount due  FROM  Customers AS cust      INNER JOIN  Payments  AS pay      ON          pay customerid   cust customerid INNER JOIN         generate a list of payment ids  their amounts  and the totals of the invoices they billed to       SELECT              inpay paymentid AS paymentid             inv invoiceid AS invoiceid              inv amount  AS inv amount              pay amount AS pay amount      FROM      InvoicePayments AS inpay         INNER JOIN      Invoices AS inv          ON  inv invoiceid   inpay invoiceid          INNER JOIN      Payments AS pay          ON pay paymentid   inpay paymentid        AS list ON      list paymentid   pay paymentid        so at this point my result set would look like       -- All my customers  crossed by  every paymentid they are associated to  I ll call this A      -- Every invoice payment and its association to  its own ammount  the total invoice ammount  its own paymentid  what I call list       -- Filter out all records in A that do not have a paymentid matching in  list       -- we filter the result because there may be payments that did not go towards invoices      GROUP BY        we want a record line for each customer and invoice   or basically each invoice but i believe this makes more sense logically             cust customernumber          list invoiceid         -- we can improve this query by only hitting the Payments table once by moving it inside of our list subquery       -- but this is what made sense to me when I was planning       -- Hopefully it makes it clearer how the thought process works to leave it in there     -- as several people have already pointed out  the data structure of the DB prevents us from looking at customers with invoices that have no payments towards them

User · Answer

Thank you very much for the replies     Saggi Malachi  that query unfortunately sums the invoice amount in cases where there is more than one payment   Say there are two payments to a  39 invoice of  18 and  12   So rather than ending up with a result that looks like   1   39 00   9 00   You ll end up with   1   78 00   48 00   Charles Bretana  in the course of trimming my query down to the simplest possible query I  stupidly  omitted an additional table  customerinvoices  which provides a link between customers and invoices   This can be used to see invoices for which payments haven t made   After much struggling  I think that the following query returns what I need it to   SELECT DISTINCT i invoiceid  i amount  ISNULL i amount - p amount  i amount  AS amountdue FROM invoices i LEFT JOIN invoicepayments ip ON i invoiceid   ip invoiceid LEFT JOIN customerinvoices ci ON i invoiceid   ci invoiceid LEFT JOIN     SELECT invoiceid  SUM p amount  amount   FROM invoicepayments ip    LEFT JOIN payments p ON ip paymentid   p paymentid   GROUP BY ip invoiceid   p ON p invoiceid   ip invoiceid LEFT JOIN payments p2 ON ip paymentid   p2 paymentid LEFT JOIN customers c ON ci customerid   c customerid WHERE c customernumber  100    Would you guys concur

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