Question

Hopefully I can do this without writing a book… I’m working on a system for a Surveying company. They’re also throwing in an accounting section, and one of the functionalities it needs is to find jobs that are not completely paid off.

A few points to be made:

• A ‘job’ is a project, essentially. There are different types of surveys.
• A job can have more than one “type” of survey in it, thus having more than one price that is calculated into the job’s total price.
• Payments are made on individual jobs (the client might send 30 checks if they have 30 jobs, it’s an accounting thing)
• Job types are dynamic (they can create/delete them from the system panel) – so I can’t hardcode these things

Here’s the applicable database structure:

table jobs: job_id, client_id
table job_types: type_id, type_name
table job_type_assoc: id_job, type_id, price
table payments: payment_id, job_id, amount

Note: payments aren’t made on each job type, but the JOB as a whole (again, as opposed to the client’s account having a “balance”).

I need to somehow pull jobs where the total of price from job_type_assoc is less than the total of amount in payments.

I don’t know if this is possible in mysql alone or if php would be more efficient – also, their old system has about 340,000 jobs in it. Granted that they won’t have the accounting info from then, they do have a lot of work and the new entries will build quickly, AND if I somehow do it in PHP where I end up querying the jobs table a lot, it might get messy.

Answer 1

One possible way you can do this is with a clever combination of subqueries.

select * from 
  (select job_id,
    (select ifnull(sum(job_type_assoc.price),0) from job_type_assoc
       where jobs.job_id = job_type_assoc.id_job) as amount_due,
    (select ifnull(sum(payments.amount),0) from payments
       where jobs.job_id = payments.job_id) as payments
    from jobs) as outstanding
  where payments< amount_due;

This shouldn’t be too bad a query to run, if you have properly indexed job_type_assoc and payments.

Please note that I haven’t tested this exact query, so it might need tweaking. I’ve run the same query against tables on my local DB.