title: How does bigquery partition selection work
body: <p>I'm confused about BigQuery's table partitioning.</p>
  <p>I have an example table with the following structure:</p>
  <pre class="lang-sql prettyprint-override"><code>CREATE TABLE `MYDATASET.MYTABLE` (
      MYCOLUMN STRING
     ,MYPARTITION TIMESTAMP
      )
  PARTITION BY DATE(MYPARTITION)
  ;
  </code></pre>
  <p>Then, I'm currently querying it like this:</p>
  <pre class="lang-sql prettyprint-override"><code>SELECT MYCOLUMN 
  FROM MYDATASET.MYTABLE 
  WHERE EXTRACT(DATE FROM MYPARTITION AT TIME ZONE 'America/Sao_Paulo') = EXTRACT(DATE FROM CURRENT_TIMESTAMP() AT TIME ZONE 'America/Sao_Paulo')
  </code></pre>
  <p>The intended result of this query is to return all rows for the current day in a specified time zone.</p>
  <p>Am I taking advantage of BigQuery partitioning with my current table structure and query? How BigQuery chooses which partitions to load?</p>
  <p>Thanks in advance.</p>