Re: Question on pgsql optimisation of SQL and structure (index, etc)

[Josh Berkus <josh@xxxxxxxxxxxx>]

Alexandre,

> -- Assuming those tables (not original, but enought to get the point):
>
> CREATE TABLE prod.jobs (
> job_id          serial   PRIMARY KEY,
> order_id        integer  NOT NULL REFERENCES sales.orders,
> );
>
> CREATE TABLE design.products (
> product_id          serial      PRIMARY KEY,
> company_id          integer     NOT NULL REFERENCES sales.companies ON
> UPDATE CASCADE,
> product_code        varchar(24) NOT NULL,
> CONSTRAINT product_code_already_used_for_this_company UNIQUE
> (company_id, product_code)
> );
>
> CREATE TABLE prod.jobs_products (
> product_id    integer     REFERENCES design.products ON UPDATE CASCADE,
> ) INHERITS (prod.jobs);

First off, let me say that I find this schema rather bizarre.  The standard 
way to handle your situation would be to add a join table instead of 
inheritance for jobs_products:

CREATE TABLE jobs_products (
	job_id INT NOT NULL REFERENCES prod.jobs(job_id) ON DELETE CASCADE,
	product_id    INT NOT NULL  REFERENCES design.products(product_id) ON UPDATE 
CASCADE,
	CONSTRAINT jobs_products_pk PRIMARY KEY (job_id, product_id)
);

Then this view:

> CREATE VIEW prod.orders_jobs_view AS
>   SELECT job_id, order_id, product_code
>     FROM (
>       SELECT *, NULL AS product_id FROM ONLY prod.jobs
>       UNION
>       SELECT * FROM prod.jobs_products
>     ) AS alljobs LEFT JOIN design.products ON alljobs.product_id =
> products.product_id;

Becomes much simpler, and better performance:

CREATE VIEW prod.orders_jobs_view AS 
SELECT job_id, order_id, product_code
FROM prod.jobs LEFT JOIN prod.jobs_products ON prod.jobs.job_id = 
prod.jobs_products.job_id
	LEFT JOIN design.products ON prod.jobs_products.product_id = 
design.products.product_id;

> I imagine that somewhere down the road, this will get slow since there
> is no index on the order_id. I tought of creating two indexes... With
> the previous VIEW and database schema, will the following boost the
> DB; as I don't know how PostgreSQL works internally:

Yes.  Any time you have a foreign key, you should index it unless you have a 
really good reason not to.

-- 
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco