https://gnarlyware.com/tags/sql/ Recent content in sql on gnarlyware Hugo -- gohugo.io fredrik.pj.nilsson@gmail.com (Fredrik Nilsson) fredrik.pj.nilsson@gmail.com (Fredrik Nilsson) Sat, 28 Aug 2021 00:00:00 +0000 https://gnarlyware.com/blog/qualify-clause-is-now-available-in-bigquery/ Sat, 28 Aug 2021 00:00:00 +0000 fredrik.pj.nilsson@gmail.com (Fredrik Nilsson) https://gnarlyware.com/blog/qualify-clause-is-now-available-in-bigquery/ <script src="{{< blogdown/postref >}}index_files/header-attrs/header-attrs.js"></script> <p>When browsing the <a href="https://cloud.google.com/bigquery/docs/reference/standard-sql/query-syntax#qualify_clause">BigQuery docs</a>, I discovered that BigQuery now supports the <code>QUALIFY</code>-clause. At time of writing, it’s in <a href="https://cloud.google.com/products#product-launch-stages">preview</a>, but you can already try it out.</p> <p>The <code>QUALIFY</code>-clause lets you filter on the output of <a href="https://cloud.google.com/bigquery/docs/reference/standard-sql/analytic-function-concepts">analytic functions</a>. This allows me to scratch an itch I’ve had for a while:</p> <div id="for-each-distinct-value-in-column-x-find-the-row-with-max-value-in-column-y" class="section level2"> <h2>For each distinct value in column X, find the row with max value in column Y</h2> <p>A common pattern is: “For each distinct value in column X, find the row where column Y takes it’s maximum value”. You can accomplish this by using <code>ROW_NUMBER() OVER (PARTITION BY X ORDER BY Y DESC) AS rank</code>.</p> <p>An example of this would be to <strong>find the date at which each of a set of countries reported the largest number of new confirmed covid-19 cases</strong>. We’ll be using the <code>bigquery-public-data.covid19_open_data</code> dataset.</p>