title: How do I select the first element in a the table returned by a SQL function
body: <p>Suppose I have a SQL function that returns a table and I get the table with</p>
  
  <pre><code>SELECT * FROM my_function('x','y');
  </code></pre>
  
  <p>Suppose that I want to write a query that returns a scalar value of the first column value in the first row returned by `my_function('x','y').</p>
  
  <p>What is the query to do that?</p>