Easy form of "insert if it isn't already there"?

From: Chris Angelico <rosuav(at)gmail(dot)com>
To: pgsql-general(at)postgresql(dot)org
Subject: Easy form of "insert if it isn't already there"?
Date: 2012-02-15 05:49:40
Message-ID: CAPTjJmrZHz6X1VnadY1WQytsRTVK4Z-auQaLeJZ29o0-Esg9kw@mail.gmail.com
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Periodically I find myself wanting to insert into some table,
specifying the primary key column(s), but to simply ignore the request
if it's already there. Currently I have two options:

1) Do the insert as normal, but suppress errors.
SAVEPOINT foo;
INSERT INTO table (col1,col2,col3) VALUES (val1,val2,val3);
(if error) ROLLBACK TO SAVEPOINT foo;

2) Use INSERT... SELECT:
INSERT INTO table (col1,col2,col3) SELECT val1,val2,val3 WHERE NOT
EXISTS (SELECT * FROM table WHERE col1=val1 AND col2=val2)

The former makes unnecessary log entries, the latter feels clunky. Is
there some better way?

All tips appreciated!

Chris Angelico

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