Re: Why is this a cross join? - Mailing list pgsql-general

From Tim Uckun
Subject Re: Why is this a cross join?
Date
Msg-id CAGuHJrMD6inC5mqiGg1Jh2R7dBJbM6rqW+q3UeYHNi68+oT6ng@mail.gmail.com
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In response to Re: Why is this a cross join?  (Tony Theodore <tony.theodore@gmail.com>)
Responses Re: Why is this a cross join?  (Adrian Klaver <adrian.klaver@gmail.com>)
Re: Why is this a cross join?  (Tony Theodore <tony.theodore@gmail.com>)
Re: Why is this a cross join?  (John R Pierce <pierce@hogranch.com>)
Re: Why is this a cross join?  (Kevin Grittner <kgrittn@ymail.com>)
List pgsql-general
>
> In some way, every join is a cross join, with the results filtered according to the specificity of the join
conditions.In this case: 
>
> inner join model_configurations mc on left(crm.customer_class, 6) = left(mc.sap_code,6)
>
> "customer_class" sounds like a fairly generic sort of field, so you'd expect many matches. Truncating the fields is
likelyto make this even less specific, returning more results. 
>

I guess I am not explaining it properly..

Say I created new columns on both tables called "first_6" and
populated them with the substrings.  If I did a inner join or a left
join on those fields would I still get a cross join?

inner join model_configurations mc on mc.first_6 = crm.first_6

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