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Message-ID: <e9c163070606011104w1d0cf7a6jca8cf5b36f2d8de3@mail.gmail.com>
Date: Thu, 1 Jun 2006 14:04:46 -0400
From: "Michael Artz" <mlartz@gmail.com>
To: "Jim C. Nasby" <jnasby@pervasive.com>
Subject: Re: Bulk loading/merging
Cc: pgsql-performance@postgresql.org
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On 5/30/06, Jim C. Nasby <jnasby@pervasive.com> wrote:

> Your best bet is to do this as a single, bulk operation if possible.
> That way you can simply do an UPDATE ... WHERE EXISTS followed by an
> INSERT ... SELECT ... WHERE NOT EXISTS.



 hmm, I don't quite understand what you are saying and I think my
basic misunderstanding is how to use the UPDATE ... WHERE EXISTS to merge
data in bulk.  Assuming that I bulk COPYed the data into a temporary
table, I'd need to issue an UPDATE for each row in the newly created table,
right?

For example, for a slightly different key,count schema:

CREATE TABLE kc (key integer, count integer);

and wanting to merge the following data by just updating the count for a
given key to the equivalent of OLD.count + NEW.count:

1,10
2,15
3,45
1,30

How would I go about using UPDATE ... WHERE EXISTS to update the "master" kc
table from a (temporary) table loaded with the above data?

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<div><span class="gmail_quote">On 5/30/06, <b class="gmail_sendername">Jim C. Nasby</b> &lt;<a href="mailto:jnasby@pervasive.com">jnasby@pervasive.com</a>&gt; wrote:</span></div>
<div>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">Your best bet is to do this as a single, bulk operation if possible.<br>That way you can simply do an UPDATE ... WHERE EXISTS followed by an
<br>INSERT ... SELECT ... WHERE NOT EXISTS.</blockquote>
<div>&nbsp;</div>
<div>&nbsp;</div>
<div>
<div>hmm, I don't quite understand what you are saying and I think my basic&nbsp;misunderstanding is how to use the UPDATE&nbsp;... WHERE EXISTS to merge data in bulk.&nbsp; Assuming that I bulk COPYed the data into a temporary table,&nbsp;I'd need to issue an UPDATE&nbsp;for each row in the newly created table, right?&nbsp; 
</div>
<div>&nbsp;</div>
<div>For example, for a slightly different key,count schema:</div>
<div>&nbsp;</div>
<div>CREATE TABLE kc (key integer, count integer);</div>
<div>&nbsp;</div>
<div>and wanting to merge the following data by just updating the count for a given key to the equivalent of OLD.count + NEW.count:</div>
<div>&nbsp;</div>
<div>1,10</div>
<div>2,15</div>
<div>3,45</div>
<div>1,30</div>
<div>&nbsp;</div>
<div>How would I go about using UPDATE ... WHERE EXISTS to update the &quot;master&quot; kc table from a (temporary) table loaded with the above data?</div>
<div>&nbsp;</div></div>
<div>&nbsp;</div></div>

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