title: Bigquery clustering not reducing query costs
body: <p><br>
  Im having an issue with clustered tables in BigQuery (with date partitions). I have a table that is clustered by a column named <strong>entity_id</strong>. The thing is, i expect to see a bytes read reduction when making queries filtered by these clustered column, but according with the BigQuery Web UI it's doing a fullscan anyway.</p>
  
  <p>For example:<br>
  SELECT * FROM <code>project.usersDataset.users_cluster</code> WHERE <strong>entity_id = '405849241'</strong> LIMIT 1000;<br>
  Returns:
  "Query complete (0.570 sec elapsed, <strong>862.94 MB</strong> processed)"<br>
  This is actually the full table size (<strong>862,94 MB</strong>)</p>
  
  <p>This is the table configuration:
  <a href="https://i.stack.imgur.com/w8axG.png" rel="nofollow noreferrer">Table configuration img</a></p>
  
  <p>EDIT: I keep going on tests and i found that sometimes, some bytes read are saved, but not too much:<br>
  <a href="https://i.stack.imgur.com/NEV4v.png" rel="nofollow noreferrer">Query from BigQuery Web Ui</a>
  I was expecting a bigger amount of bytes cost to be saved (returned 1 entry and scanned 719MB of 862MB of the table) but nothing guaranteed these in the bigquery documentation.</p>
  
  <p>Does anyone have a clue on what could be happening?<br>
  Thanks!</p>