title: Postgres: user mapping not found for "postgres"
body: <p>I'm connected to schema <code>apm</code>.</p>
  <p>Trying to execute a function and getting below error:</p>
  <pre><code>ERROR:  user mapping not found for &quot;postgres&quot;
  </code></pre>
  <p>Database connection info says:</p>
  <pre><code>apm on postgres@PostgreSQL 9.6
  
  psql version: PostgreSQL 9.6.3, compiled by Visual C++ build 1800, 64-bit
  </code></pre>
  <p>How can this error be addressed?</p>