MySQL - Select unique column with max timestamp
<p>I'm trying to prepare a query and I'm having a hard time with it. I need some MySQL gurus to help please...</p>

<p>Take the following table as an example...</p>

<p><code>
CREATE TABLE <code>order_revision</code> (
  <code>id</code> int(11) NOT NULL,
  <code>parent_order_id</code> int(11) NOT NULL,
  <code>user_id</code> int(11) DEFAULT NULL,
  <code>sub_total</code> decimal(19,4) NOT NULL DEFAULT '0.0000',
  <code>tax_total</code> decimal(19,4) NOT NULL DEFAULT '0.0000',
  <code>status</code> smallint(6) NOT NULL DEFAULT '1',
  <code>created_at</code> int(11) NOT NULL,
  <code>updated_at</code> int(11) DEFAULT NULL
)
</code></p>

<p>I need a query to select all unique 'parent_order_id' with the max 'updated_at' value. This query should return all rows that have unique 'parent_order_id's based on the max timestamp of the 'updated_at' column. </p>

<p>In other words, each row returned should have an unique 'parent_order_id' and be the maximum timestamp of the'updated_at' column.</p>

<p>Basically this query would find the latest "order revision" for each "parent order"</p>