title: Correlated subqueries that reference other tables are not supported
body: <p>I have hundreds of queries powering dashboards at my company that have worked for years but broke overnight a couple days ago giving the error:</p>
  
  <blockquote>
    <p>Error: Correlated subqueries that reference other tables are not supported unless they can be de-correlated, such as by transforming them into an efficient JOIN.</p>
  </blockquote>
  
  <p>Below is an example of the type of query that has the issue. Obviously the WHERE condition is the problem. Is this type of query really no longer going to be supported? Will all queries with this syntax now need to be converted to use an INNER JOIN? This is a huge change that has really impacted our analytics.</p>
  
  <pre><code>-- standardSQL
  SELECT 
    accounts,
    monthly_timestamp
  FROM 
    `custom_query_ingestion.accounts_monthly`
  WHERE 
    monthly_timestamp &lt;= (SELECT MAX(TIMESTAMP(date)) FROM `historical_data.historical_revenue`) 
  </code></pre>