RE: mysql's "replace into..." - Mailing list pgsql-sql

Thanx for your help.  I found replace into to be a nice convience since my
primary keys are often expressions build from several fields which I want to
keep unique.  Replace into enforces this uniqueness.  I was learning SQL
when I started this project so I didn't know this was non-standard.  Bummer.

But since my primary keys are expressions, I can't use the technique you
suggested.  I'm thinking of simply trying the insert and checking to see if
I get an error.  If I get an error, I do an update...  Not sure how well
this will work, tho.

Any suggestions?

Thanx for your time.

-----Original Message-----
From: Josh Berkus
To: Diehl, Jeffrey
Cc: 'pgsql-sql@postgreSQL.org'
Sent: 2/28/01 12:56 PM
Subject: Re: [SQL] mysql's "replace into..."

Jeff,

> I'm in the process of migrating a production database and related
> applicatoins from mysql to postgresql.  I've just not been very
impressed
> with mysql's stability, that is I'm trying to make my phone stop
ringing.

Surprising.  I have a number of gripes with MySQL (of which REPLACE INTO
is one), but stability isn't one of them.

> However, when I wrote the applications, I took free advantage of
mysql's
> replace into feature which behaves like a smart insert that inserts
new
> records or updates old records.  I'm using perl DBI and need to figure
out a
> good way to migrate this to postgresql.
> 
> Any ideas?

Well, you have two choices.  One is to get used to standard SQL and use
the SQL I will expound below.  The other is to actually hire a C
programmer to modify the PostgreSQL source to support Replace Into. 
Great Bridge might be willing to help.

Regardless, your SQL functionality requires the following steps:

1. All tables involved *must* have primary keys.  I reccommend against
using the OID for this purpose for several reasons; see the archives for
a discussion.

2. Build an if-then stucture for your update calls, that goes like this
(this assumes that your primary key is SERIAL):
IF primarykey_variable = 0 THENINSERT INTO table1 (field1, field2, field3)VALUES (variable1, variable2, variable3);
ELSEUPDATE table1 SET field1 = variable1,    field2 = variable2,    field3 = variable3WHERE primarykey =
primarykey_variable;
END IF;

-Josh Berkus

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