Doing a conditional insert/update

Hello.<br /><br />I'm currently developing my first web app with Postgres and I have a question. <br /><br />How do I
performa conditional insert/update? <br /><br />To clarify: I need to insert data into a table when the primary key is
notalready in the table, or an update if it is. I have currently solved this by SELECTing for the primary key, then
lookingif there is a row, and if there is I do an UPDATE otherwise I do an INSERT. But since this is a web app this way
ofcourse leaves a big race condition. <br /><br />Is there a way to get around that? Like the ON DUPLICATE KEY UPDATE
statementin MySQL?<br /><br /><br />Thanks for your time,<br /><br />Holli<span style="font-family: monospace;"><br
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