this question goes on from my previous one about my 1st hurdle using SQLite3. what sort of performance hit will you get if you have 3 select statements (1 for each table/DB file)? tables are customer, Jobs, parts. customer has a unique field called customer number. Jobs has a field for the customer number in it and a unique field called Job number. lastly parts has a field called job number. not sure how many rows there might be for a customer and rows for parts at present. but really I'm more concerned with getting everything playing in tune and then when I'm more familiar wit SQLite look at optimizations like using joins. an yes ultimately i may move off sqlite to another DB but that's another step. Oh also all this is via DBI. Active record will be another stepping stone (Feel like I've got too much to cope with for now but perhaps ultimatly go to active record too). cheers, dave.
on 2009-06-08 13:28
on 2009-06-08 14:04
I would always recommend using the database to perform joins. People have spent thousands of hours (perhaps incorporating the work of millions of other peoples' hours) in designing the database to optimise joins, so why would you possibly want to reinvent that wheel? From what I've seen of ActiveRecord, it has some way of expressing relationships but I'm a bit dubious about the whole object-relation mapping model. Database-centric approaches have worked for big complex systems for decades so why force the issue.
on 2009-06-08 14:08
I don't use SQLite, I'm more of a SQl heavy (DB2, Postgresql, Oracle) type. What you're asking for is a plain old, b-flat, vanilla join. I don't know why you'd be doing this in three separate queries. Without seeing your schema, or knowing exactly which columns you want to pull, I'll use '*', which cats all columns in all tables. I assuming you have a part_number in parts (or maybe a part_name.) Select * from customer, jobs, parts where customer.customer_number = jobs.customer_number and jobs.job_number = parts.job_number order by customer.customer_number, jobs.job_number, parts.part_number This should be quite efficient if there are indexes on jobs.customer_number and parts.job_number, otherwise a sequential scan will be needed for each of the two joins, and that will kill you. > but really I'm more concerned with getting everything playing in tune > and then when I'm more familiar wit SQLite look at optimizations like > using joins. I suggest you do the hard work up front. It will save you a lot of bad design decisions down the line. Good luck, Bob Schaaf
on 2009-06-08 15:23
On second thought, it doesn't look like your schema does what it ought to. You'd think that any customer can contract for a certain job which requires specific parts which can be used in other jobs. If so, you'd need 1. a customer table with unique records for each customer, identified by customer_number; 2. a jobs table describing a job, with a unique key for job_number; 3. a parts table describing a part, with a unique key for part_number; THEN you need the join tables. 4. a contracts table, with a unique key on contract_number, and an index on customer_number; 5. a bill_of_parts table, indexed uniquely on job_number. Then the join would be customers.customer_number = contracts.cusomer_number contracts.job_number = jobs.job_number jobs.job_number = bill_of_parts.job_number bill_of_parts.part_number = parts.part_number This too is trivial, and should be quick if your RDB isn't a complete dog. I don't know of SQLite permits multi-column keys and indexes, so perhaps, "Woof, woof!" BS