Re: Outer Right Join?

First problem is the database design is no good.

1. If companies <—> products is many-to-many, you need a cross-reference table between them.
2. If companies <—> contracts is one-to-one, optional, then contracts should be a list of contracts (not of companies), or, if there are no significant attributes of a contract, merged into companies as a status flag or boolean (is there a contract with this company or not?).

It is almost never a good idea to have the same entity (in this case, companies) stored in more than one table solely because of varying attribute or relationship values.

It’s not a good idea to try to twist SQL into compensating for a confused database design.

Note: There is no way that SELECT DISTINCT needs to be part of your solution.

You might want to have a look at a book such as this one:

https://www.amazon.com/Data-Analysis-Database-Design-David/dp/0750650869 <https://www.amazon.com/Data-Analysis-Database-Design-David/dp/0750650869>

Cheers,

Mark

> On Feb 20, 2020, at 03:04, Bee.Lists <bee(dot)lists(at)gmail(dot)com> wrote:
>
> I’m looking for a three-table join. The SQL that I have isn’t working.
>
> companies table - list of companies
> products table - list of products sold by those companies
> contracts table - list of companies that hold ad contracts
>
> I need to ask:
>
> "Show me the queried product (i.e.: Screwdriver) listings with their company names that DO NOT have contracts"
>
> SELECT DISTINCT ON ("listings"."product")
> "listings"."product", "companies"."name"
> FROM "listings"
> RIGHT OUTER JOIN "contracts" ON ("contracts"."companyid" = "listings"."companyid")
> LEFT JOIN "companies" ON ("companies"."scid" = "listings"."companyid")
> WHERE (("listings"."product" ILIKE '%screwdriver%' ESCAPE '\'))
>
> The result works without the RIGHT OUTER JOIN in there. When the RIGHT OUTER JOIN is in there, I get a hitlist of zero. Currently I have no contracts in that table, so those two queries should be the same. They are not.
>
> To repeat, I want any company’s products that are in the contracts table, to not show up. “products with no contract”.
>
> Any inside as to how I can get this to work, appreciated.
>
>
> Cheers, Bee
>
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