title: Uncommitted read SQL
body: <p>I have a question about uncommitted read. I understand that it is used for setting transaction isolation levels. But I am trying to understand a query which is as follows:</p>
  
  <pre><code>    SELECT * 
      FROM customer_records as c, transaction_records as t 
      WHERE e.customer_id= t.customer_id 
  union
      SELECT *
      FROM customer_records as c, transaction_records as t 
      WHERE e.customer_id= t.customer_id with ur;
  </code></pre>
  
  <p>As I understand it, this query is doing a union between already committed and uncommitted data for the records in both tables. Could someone elaborate on what would be the use of such data? And whether I am understanding the query correctly, as I think that <code>ur</code> is applied to second query only?</p>