Re: Problem with left join when moving a column to another table

Jason Long-2 wrote
>> Jason Long-2 wrote
>
>
> There is a unique constraint on the real price table.  I hadn't thought
> of how I will enforce the constraint across two tables.
> size_id and area_id will have to be unique across both
> t_price_base_table and t_price_original_with_area_id.  I will want to
> drop area_id from t_price_original_with_area_id.
>
> What is the best way to implement the cross table unique constraint?

Don't.

If size+area is a unique constraint then there should be a table that
defines valid pairs and creates a PRIMARY KEY over them.

Per my original comment your issue isn't JOINs (well, your biggest issue
anyway) but your model.  The fact that you couldn't write a good query
simply exposed the problems in the model.  This is not uncommon.

I would need a lot more information (and time) than I have now to offer any
design thoughts on your schema; though I do find the unique constraint over
size+area to be unusual - as well as using that as a foreign key from the
item table.  You haven't specified the domain for this model but using homes
as an example I would use a 'model' table with "model_id, size, area" as
columns.  A particular house would then link in "model" and "price".  You
could possibly further restrict that certain models can only sell for
certain prices if necessary - in which case you would have "model_price" and
possibly "house_model_price" tables (the later could be an FK).

David J.








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