Обсуждение: two foreign keys

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?

-----

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

______AGLIO DATABASE SOLUTIONS___________________________
                                       Josh Berkus
  Complete information technology      josh@agliodbs.com
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"Josh Berkus" <josh@agliodbs.com> writes:
> 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;

I think you meant "ON sessions.operator_end_id = op_end.operator_id"
at the end there.  Otherwise a fine example...

            regards, tom lane

I just upgraded to RedHat 7.2 and I'm having a problem starting the postmaster with the -i argument for tcpip.

The /etc/rd.d/init.d/postgresql file has a line in it like this:


su -l postgres -s /bin/sh -c "/usr/bin/pg_ctl -D $PGDATA -p /usr/bin/postmaster start  > /dev/null 2>&1" < /dev/null

if I insert an -i before the -D... or after it... or behind the -p or where ever it fails.

have been messing with the script... trying different things that I find in the documentation, some of it from my
imagination.Some of it works... but hangs the boot process at startup 

What's the correct way to do this?

thanks,
Brian

On Thursday 07 March 2002 20:08, Brian wrote:
> I just upgraded to RedHat 7.2 and I'm having a problem starting the postmaster with the -i argument for tcpip.
>
> The /etc/rd.d/init.d/postgresql file has a line in it like this:
>
>
> su -l postgres -s /bin/sh -c "/usr/bin/pg_ctl -D $PGDATA -p /usr/bin/postmaster start  > /dev/null 2>&1" < /dev/null
>
> if I insert an -i before the -D... or after it... or behind the -p or where ever it fails.

Try:

su -l postgres -s /bin/sh -c "/usr/bin/pg_ctl -D $PGDATA -p '/usr/bin/postmaster -i' start  > /dev/null 2>&1" <
/dev/null

Regards
JohnT

Hi John,

I am getting a FAILED notice on your construction.

if I delete the   >/dev/null 2>&1   I can see:

/usr/bin/pg_ctl: /usr/bin/postmaster -i: No such file or directory

as a response...

so I tried removing the single quotes ' and I get this as a response:

starting service pg_ctl: invalid option: -i

-------
still struggling here,
Brian




At 10:13 PM 3/7/02 +0000, John Taylor wrote:
>On Thursday 07 March 2002 20:08, Brian wrote:
>> I just upgraded to RedHat 7.2 and I'm having a problem starting the postmaster with the -i argument for tcpip.
>>
>> The /etc/rd.d/init.d/postgresql file has a line in it like this:
>>
>>
>> su -l postgres -s /bin/sh -c "/usr/bin/pg_ctl -D $PGDATA -p /usr/bin/postmaster start  > /dev/null 2>&1" < /dev/null
>>
>> if I insert an -i before the -D... or after it... or behind the -p or where ever it fails.
>
>Try:
>
>su -l postgres -s /bin/sh -c "/usr/bin/pg_ctl -D $PGDATA -p '/usr/bin/postmaster -i' start  > /dev/null 2>&1" <
/dev/null
>
>Regards
>JohnT