title: Select from bigquery based on more nested columns
body: <p>I need to filter by more nested data in bigquery and I am only able to filter with my query by one.</p>
  
  <p>Basically i need this:</p>
  
  <pre><code>SELECT item_id FROM table WHERE item_id IS NOT NULL AND page_id = '23784'
  </code></pre>
  
  <p>Is such thing possible?</p>
  
  <p>I have data in bigquery like below, page_id doesn't have to exist:</p>
  
  <pre><code>| row | date | event      | params.key    | params.value |
  -------------------------------------------------------
  | 1   | 2018 | screenShow | item_id       | 1            |
                            | page_id       | 23784        |
                            | irrelevant_id | 5            |
  | 2   | 2018 | screenShow | item_id       | 2            |
                            | irrelevant_id | 7            |
  </code></pre>
  
  <p>My query is:</p>
  
  <pre><code>SELECT param.value
  FROM `table`,
  UNNEST(params) AS param
  WHERE
      event = 'screenShow'
      AND param.key = 'item_id'
  </code></pre>
  
  <p>but this obviously works only for one key and i don't know how to add the page_id part.
  Thanks.</p>