From: Josh Berkus <josh@agliodbs.com>
To: Beth Gatewood <beth@vizxlabs.com>
To: pgsql-sql@postgresql.org
Subject: Re: writing a function to mimic mysql last_insert_id
Date: Wed, 11 Sep 2002 10:53:49 -0700
Message-ID: <200209111053.49837.josh@agliodbs.com> (raw)
In-Reply-To: <000901c259ba$c5b7ee70$0c00000a@bethvizx>
References: <000901c259ba$c5b7ee70$0c00000a@bethvizx>
Beth,
> However, we are in the midst of porting a mysql database to pgsql. The perl
> application that is tied to this mysql database heavily utilizes
> last_insert_id. In an effort to save the perl developers the pain of having
> to go in and modify a bunch of their SQL to call out to seq.currval, I
> thought I would attempt to mimic this function.
>
> Perhaps there is another way to approach this than writing this type of
> function?
Not really. CURRVAL requires a sequence name as a parameter because, in
Postgres, one can have more than one sequence for a table. Further, in
Postgres, you can update more than one table at a time using a function,
trigger, or rule; how would any function know which sequence id to return?
While it would be relatively easy for a function to look up what seqeunces
were related to a table in the pg_* tables, you are left with the difficult
task of determining what statement the user last ran. This would, I think,
involve hacking MVCC to some degree.
If you're serious about pursuing this, I suggest posting your question on
PGSQL-HACKERS to get help with hacking MVCC to determine a connection's last
action. I have no idea how easy or difficult this would be.
A second possibility would be writing triggers for all tables that place a
value into a temporary table that can be read back by your custom function.
You may find it less work, however, to do a search-and-replace on calls to
last_inser_id(). But if you do write a replacement function, please post it
on TechDocs!
--
-Josh Berkus
Aglio Database Solutions
San Francisco
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To: pgsql-sql@postgresql.org
Cc: josh@agliodbs.com, beth@vizxlabs.com
Subject: Re: writing a function to mimic mysql last_insert_id
In-Reply-To: <200209111053.49837.josh@agliodbs.com>
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