mysql - Combine Sum with select join and union -


i need join 2 query this

select * contracts join customers on customer.id=contracts.customer

and (12234 explample customer)

select *,sum(cast(amount unsigned)) total from(     select * invoices customer='123456' union select * paypal_invoices customer='123456') t1

in first query extract normal customers list based on actives contracts have.

in second extract sum of invoice specific customers

so need extract customers first query need column sum of invoice specific customer. thank you.

one method correlated subqueries or left joins:

select co.*, cu.*, i.amount, pi.amount paypal_amount,        ( coalesce(i.amount, 0) + coalesce(pi.amount, 0) ) total        contracts co join      customers cu      on cu.id = co.customer left join      (select customer, sum(amount) amount       invoices       group customer      )      on i.customer = cu.id left join      (select customer, sum(amount) amount       paypal_invoices       group customer      ) pi      on pi.customer = cu.id;

two key ideas here. first, sure aggregate before doing joins. prevents joins multiplying number of rows , generating incorrect results. similarly, uses left join ensure customers included, no invoices.

second idea: don't use union. query, in fact, possibly incorrect. union removes duplicates -- both within table , between tables. safer use union all. or, in case, not needed @ all.


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