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    <p><strong>Short Answer:</strong></p> <p>MERGE INTO AUDIT_TRANSACTION_IDS (uuid, time) KEY (uuid, time) VALUES (TRANSACTION_ID(), NOW()); </p> <p><sub>little performance tip: make sure uuid is indexed</sub></p> <p><strong>Long Answer:</strong></p> <p><code>MERGE</code> is basically an <code>UPDATE</code> which <code>INSERT</code>s when no record found to be updated. </p> <p>Wikipedia gives a more concise, standardized syntax of <a href="http://en.wikipedia.org/wiki/Merge_%28SQL%29" rel="nofollow">MERGE</a> but you have to supply your own update and insert. (Whether this will be supported in H2 or not is not mine to answer) </p> <p>So how do you update a record using <code>MERGE</code> in H2? You define a key to be looked up for, if it is found you update the row (with column names you supply, and you can define <code>DEFAULT</code> here, to reset your columns to its defaults), otherwise you insert the row. </p> <p>Now what is <code>Null</code>? <code>Null</code> means unknown, not found, undefined, anything which is not what you're looking for. </p> <p>That is why <code>Null</code> works as key to be looked up for. Because it means the record is not found. </p> <blockquote> <p>MERGE INTO table1 (id, col1, col2) KEY(id) VALUES (Null, 1, 2) </p> </blockquote> <p><code>Null</code> has a value. it IS a value.</p> <p>Now let's see your SQL. </p> <blockquote> <p>MERGE INTO table1 (id, col1, col2) KEY(id) VALUES (DEFAULT, 1, 2)</p> </blockquote> <p>What is that implying? To me, it says I have this [DEFAULT, 1, 2], <strong><em>find me a <code>DEFAULT</code> in column <code>id</code></em></strong>, then update <code>col1</code> to 1, <code>col2</code> to 2, if found. otherwise, insert default to <code>id</code>, 1 to <code>col1</code>, 2 to <code>col2</code>. </p> <p>See what I emphasized there? What does that even mean? What is <code>DEFAULT</code>? How do you compare <code>DEFAULT</code> to <code>id</code>? </p> <p><code>DEFAULT</code> is just a keyword. </p> <p>You can do stuff like, </p> <blockquote> <p>MERGE INTO table1 (id, col1, timeStampCol) KEY(id) VALUES (Null, 1, DEFAULT)</p> </blockquote> <p>but don't put DEFAULT in the key column.</p>
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    1. POMERGE INTO table containing AUTO_INCREMENT columns
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    1. COplease add a discussion of MERGE INTO's return value. Can Statement.getGeneratedKeys() be used to retrieve any keys?
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