Re: two foreign keys

Brian,

> I have a table that has two foreign keys to the same table.
>
> - operator_id_start
> - operator_id_stop
>
> Both point to the operator table.
>
> When displaying the row from the table how do I join so that I can
> have both Operator table details available?

Aha! I love the classic novice questions. So much easier than "I
can't get Perl::SSElay to connect with Pgsql>"

The bit of SQL knowledge you're missing is called "table aliasing."
This is where you give a table a different name in the query than its
real name. Aliasing allows you to refer to the same table more than
once in a query.

So, to answer your question, making up quite a bit of detail about your
tables that I don't have:

SELECT session_id, session_name, op_start.operator_name,
op_end.operator_name
FROM sessions
JOIN operators op_start ON sessions.operator_start_id =
op_start.operator_id
JOIN operators op_end ON sessions.operator_end_id =
op_start.operator_id;

Got it? Now go buy yourself a copy of "SQL Queries for Mere Mortals."

-Josh Berkus

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